UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 5)*

USA TRUCK, INC.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

902925106

(CUSIP Number)

Stone House Capital Management, LLC

Attn: Mark Cohen

950 Third Avenue, 17^th Floor

New York, NY 10022

(212) 543-1500

with a copy to:

Taylor H. Wilson, Esq.

Haynes and Boone, LLP

2323 Victory Avenue, Suite 700

Dallas, Texas 75219

(214) 651-5000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 5, 2015

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  x

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934, as amended (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 5 to Schedule 13D is jointly filed by and on behalf of each of the Reporting Persons to amend the Schedule 13D related to the common stock (the “Common Stock”) of USA Truck, Inc., a Delaware corporation (the “Issuer”) previously filed by the Reporting Persons with the Securities and Exchange Commission (the “Commission”) (as amended, the “Schedule 13D”). Each capitalized term used and not defined herein shall have the meaning assigned to such term in the Schedule 13D. Except as otherwise provided herein, each Item of the Schedule 13D remains unchanged.

Item 2. Identity and Background

Item 2 is hereby amended and restated in its entirety as follows:

“(a) This Schedule 13D is jointly filed by and on behalf of each of Stone House Capital Management, LLC, a Delaware limited liability company (“Stone House”); SH Capital Partners, L.P., a Delaware limited partnership (“Partners”); and Mark Cohen (“Mr. Cohen”). Stone House, Partners and Mr. Cohen are collectively referred to herein as the “Reporting Persons”. The Reporting Persons are filing this Schedule 13D jointly, and the agreement among the Reporting Persons to file jointly is attached hereto as Exhibit 99.1 and incorporated herein by reference (the “Joint Filing Agreement”). Partners is the record and direct beneficial owner of the securities covered by this statement. Stone House is the general partner of, and investment manager to, Partners. Mr. Cohen is the managing member of Stone House.

Each Reporting Person declares that neither the filing of this Schedule 13D nor anything herein shall be construed as an admission that such person is, for the purposes of Section 13(d) or 13(g) of the Act, the beneficial owner of any securities covered by this Schedule 13D.

(b) The address of the principal business office of each of the Reporting Persons is c/o Stone House Capital Management, LLC, 950 Third Avenue, 17^th Floor, New York, NY 10022.

(c) The principal business of Partners is acquiring, holding and selling securities for investment purposes. The principal business of Stone House is serving as the general partner of, and investment manager to, Partners. The present principal occupation of Mr. Cohen is serving as the managing member of Stone House.

(d) No Reporting Person has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e) No Reporting Person has, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction as a result of which such Reporting Person was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) The place of organization of each Reporting Person, other than Mr. Cohen, is listed in paragraph (a) of this Item 2. Mr. Cohen is a citizen of the United States of America.”

Item 3. Source and Amount of Funds or other Consideration

Item 3 is hereby amended and restated in its entirety as follows:

“The Reporting Persons expended an aggregate of approximately $19,574,167.08 (including commissions) to acquire 1,550,000 shares of Common Stock of the Issuer in various open market transactions. Funds used to acquire shares of Common Stock of the Issuer have come from general working capital of Partners.”

Item 4. Purpose of Transaction

Item 4 of the Schedule 13D is hereby amended to add the following:

“On May 5, 2015, the Reporting Persons entered into an Amendment to Cooperation Agreement (the “Amendment”) with the Issuer. The Amendment amends certain provisions of the previously disclosed Cooperation Agreement entered into by the Issuer and the Reporting Persons on February 25, 2015 (as amended, the “Cooperation Agreement”).

The Cooperation Agreement requires, among other things, the Issuer to undertake a public secondary offering of 600,000 shares of its Common Stock held by Partners and the Reporting Persons to reimburse the Issuer for certain expenses incurred in connection with such offering. Prior to the Amendment, the aggregate amount of expenses for which the Reporting Persons were obligated to reimburse the Issuer was capped at $18,000 and the reimbursement applied only to designated expenses. Under the Amendment, if the offering of Partners’ shares of Common Stock does not close by June 15, 2015, and certain acts or omissions of any Reporting Person have occurred, then (a) the Reporting Persons are obligated to reimburse the Issuer for an expanded portion of the expenses related to the offering, up to an aggregate amount of $200,000 and (b) the Issuer will not be obligated to undertake a future offering for the Reporting Persons until the parties reach a subsequent agreement on expense allocation and timing.

The foregoing description of the Cooperation Agreement and the Amendment does not purport to be complete and is qualified in its entirety by reference to the full text of the Cooperation Agreement and the Amendment, which are filed herewith as Exhibits 99.2 and 99.3 and are incorporated herein by reference.”

Item 5. Interest in Securities of the Issuer

Item 5 is hereby amended and restated in its entirety as follows:

“(a) The aggregate number and percentage of the class of securities identified pursuant to Item 1 beneficially owned by each Reporting Person is stated in Items 11 and 13 on the cover page(s) hereto.

Each Reporting Person declares that neither the filing of this Schedule 13D nor anything herein shall be construed as an admission that such person is, for the purposes of Section 13(d) or 13(g) of the Act or any other purpose, the beneficial owner of any securities covered by this Schedule 13D.

Each Reporting Person may be deemed to be a member of a group with respect to the Issuer or securities of the Issuer for the purposes of Section 13(d) or 13(g) of the Act. Each Reporting Person declares that neither the filing of this Schedule 13D nor anything herein shall be construed as an admission that such person is, for the purposes of Section 13(d) or 13(g) of the Act or any other purpose, (i) acting (or has agreed or is agreeing to act) with any other person as a partnership, limited partnership, syndicate or other group for the purpose of acquiring, holding or disposing of securities of the Issuer or otherwise with respect to the Issuer or any securities of the Issuer or (ii) a member of any syndicate or group with respect to the Issuer or any securities of the Issuer.

See Item 7 on the cover page(s) hereto.

See Item 8 on the cover page(s) hereto.

See Item 9 on the cover page(s) hereto.

See Item 10 on the cover page(s) hereto.

Partners is the record and direct beneficial owners of the securities covered by this Schedule 13D. Partners has the power to vote or to direct the vote of (and the power to dispose or direct the disposition of) the shares owned by it.

As general partner of Partners, Stone House may be deemed to have the shared power to vote or to direct the vote of (and the shared power to dispose or direct the disposition of) any shares of Common Stock of the Issuer beneficially owned by Partners. Stone House does not own any shares of Common Stock of the Issuer directly and disclaims beneficial ownership of any shares of Common Stock of the Issuer beneficially owned by Partners.

As the managing member of Stone House, Mr. Cohen may be deemed to have the shared power to vote or to direct the vote of (and the shared power to dispose or direct the disposition of) any shares of Common Stock of the Issuer beneficially owned by Stone House. Mr. Cohen does not own any shares of Common Stock of the Issuer directly and Mr. Cohen disclaims beneficial ownership of any shares of Common Stock of the Issuer beneficially owned by Stone House.

As of the date hereof, no Reporting Person owns any shares of Common Stock of the Issuer other than as set forth in this Item 5.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 of the Schedule 13D is hereby amended to add the following:

“The information set forth in Item 4 is incorporated by reference into this Item 6.”

Item 7. Material to be Filed as Exhibits

Item 7 of the Schedule 13D is hereby amended and restated in its entirety as follows:

“The following exhibits are filed as exhibits hereto:

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

EXHIBIT INDEX

Exhibit 99.1

JOINT FILING AGREEMENT

May 7, 2015

Pursuant to and in accordance with the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules and regulations thereunder, each party hereto hereby agrees to the joint filing, on behalf of each of them, of any filing required by such party under Section 13 or Section 16 of the Exchange Act or any rule or regulation thereunder (including any amendment, restatement, supplement, and/or exhibit thereto) with the Securities and Exchange Commission (and, if such security is registered on a national securities exchange, also with the exchange), and further agrees to the filing, furnishing, and/or incorporation by reference of this agreement as an exhibit thereto. This agreement shall remain in full force and effect until revoked by any party hereto in a signed writing provided to each other party hereto, and then only with respect to such revoking party.

IN WITNESS WHEREOF, each party hereto, being duly authorized, has caused this agreement to be executed and effective as of the date first written above.

Exhibit 99.3

AMENDMENT TO COOPERATION AGREEMENT

This AMENDMENT TO COOPERATION AGREEMENT (this “Amendment”), is made and entered into as of May 5, 2015 by and among USA Truck, Inc., a Delaware corporation, Stone House Capital Management, LLC, a Delaware limited liability company, SH Capital Partners, L.P., a Delaware limited partnership, and Mark Cohen (collectively, the “Parties”). Capitalized terms used but not otherwise defined herein shall have the meanings given to such terms in the Agreement (defined below).

WHEREAS, the Parties have entered into that certain Cooperation Agreement, dated February 25, 2015 (the “Agreement”);

WHEREAS, the Parties desire that the Agreement be amended in certain respects in accordance with the terms of this Amendment;

NOW, THEREFORE, in consideration of the premises and mutual covenants and agreements set forth herein, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties hereto hereby agree as follows:

Section 1. Amendment of Agreement.

(a) Section 1(c)(i) of the Agreement is hereby amended and restated in its entirety as follows:

“(i) The Investor shall pay, or cause to be paid, a percentage of the Offering Expenses in proportion to the ratio of the Investor Shares registered in the Offering to the total number of All Investors Shares registered in the Offering. The term “Offering Expenses” means (A) all fees, disbursements and expenses incurred in connection with the printing, reproduction and filing of any documents required in connection with the Offering, (B) all fees and expenses of the Company’s auditors incurred in connection with the Offering (but excluding such fees and expenses that arose prior to March 6, 2015), and (C) the costs and expenses of the Company relating to investor presentations on any “road show” undertaken in connection with the Offering, including without limitation expenses associated with the production of road show slides and graphics, fees and expenses of any consultants engaged in connection with the road show presentations, travel and lodging expenses of the representatives and officers of the Company and any such consultants, and the cost of aircraft and other transportation chartered in connection with the road show. For the avoidance of doubt, (X) the Company shall undertake a “road show” unless otherwise agreed by the Parties in writing, (Y) except as set forth in the next sentence the portion of the Offering Expenses to be shared pro rata by all investors who register shares in the Offering shall not exceed $60,000 and (Z) by means of example, if the Investor registers in the Offering 600,000 shares and another investor(s) registers in the Offering 1,400,000 shares, then the Investor shall be responsible for 30% of up to $60,000, or up to $18,000 and the other investor(s) will be responsible for

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70% of up to $60,000, or up to $42,000. Notwithstanding anything to the contrary, if the Offering fails to close prior to June 15, 2015, and an Investor Reason shall exist with respect to Investor, Investor will reimburse the Company within 15 days for the actual amount of the Company’s Transaction Expenses, up to $200,000 (subject, in certain circumstances, to proration as described in the next two sentences). If an Investor Reason also exists with respect to any other investor participating in the Offering, the Transaction Expenses will be shared pro rata by all investors who register shares in the Offering in proportion to the number of shares registered by each investor. By means of example, if the Investor registers in the Offering 600,000 shares and another investor(s) registers in the Offering 1,400,000 shares, then the Investor shall be responsible for 30% of up to $200,000, or up to $60,000 and the other investor(s) will be responsible for 70% of up to $200,000, or up to $140,000. “Investor Reason” means the Investor or any other investor participating in the Offering (1) contributes materially to any delay or postponement in the Offering that interferes with a closing by June 15, 2015, (2) indicates or imposes any price range or requirement or indicates an unwillingness to sell its shares for any reason, (3) fails to execute and deliver a lock-up agreement, underwriting agreement, certificate, or other document reasonably required by the underwriters or the Company in customary form, (4) fails to comply with the customary closing conditions required by the underwriting agreement, or (5) otherwise fails to cooperate in a timely and effective manner to the extent reasonable and customary for selling stockholders. However, an Investor Reason will be deemed not to exist if, prior to the first to occur of the events described in clauses (1) through (5) above, the underwriters advise the Company and the Investor in writing that they are unwilling to proceed with an Offering or are unable to place at least 75% of the Investor Shares at any price, the Company fails to comply with any closing condition of the Company (and not the selling stockholders) set forth in the underwriting agreement (which failure to comply is not waived) or terminates the Offering, or the SEC shall issue any stop order or similar halt or restriction on the Offering. “Transaction Expenses” means all of the Company’s fees and expenses incurred in connection with an Offering, including without limitation Offering Expenses, attorneys’ fees and expenses, and expenses associated with due diligence and closing, incurred by the Company from and after April 20, 2015.”

(b) The following paragraph is hereby added to the Agreement as Section 1(d):

“(d) If the Offering fails to close prior to June 15, 2015, and an Investor Reason shall exist with respect to Investor, the Company will not be obligated to undertake any future Offering on behalf of the Investor or any Affiliate unless the Parties reach a subsequent written agreement as to Transaction Expenses in connection with such future Offering and the Company and the underwriters agree on the timing of such future Offering.”

Section 2. Consent. Investor hereby consents to the Company’s public disclosure of this Amendment and the terms hereof in a manner consistent with the Company’s prior disclosure of the Agreement, as required by law and stock exchange regulation, and as necessary or advisable in connection with the Offering.

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Section 3. Representations and Warranties. Each of the Company and Investor hereby remake the representations and warranties contained in Section 5 and Section 6 of the Agreement, respectively; provided, that any such representations and warranties made with respect to the Agreement are instead made with respect to this Amendment.

Section 4. Effect on Agreement. Except as specifically amended hereby, the terms and provisions of the Agreement are, in all other respects, ratified and confirmed and remain in full force and effect. Except as expressly set forth herein, the amendments provided herein shall not by implication or otherwise limit, constitute a waiver of, or otherwise affect the rights and remedies of the Parties with respect to the Agreement. No reference to this Amendment need be made in any notice, writing, or other communication relating to the Agreement, any such reference to the Agreement to be deemed a reference thereto as amended by this Amendment. All references to the Agreement in any document, instrument, or agreement executed in connection with the Agreement will be deemed to refer to the Agreement as amended hereby.

Section 5. Governing Law. This Amendment shall be governed by, and construed in accordance with, the Law of the State of Delaware, without regard to conflict of law principles thereof.

Section 6. Waiver of Jury Trial. EACH PARTY ACKNOWLEDGES AND AGREES THAT ANY CONTROVERSY WHICH MAY ARISE UNDER THIS AMENDMENT IS LIKELY TO INVOLVE COMPLICATED AND DIFFICULT ISSUES AND, THEREFORE, EACH SUCH PARTY IRREVOCABLY AND UNCONDITIONALLY WAIVES ANY RIGHT IT MAY HAVE TO A TRIAL BY JURY IN RESPECT OF ANY LEGAL ACTION DIRECTLY OR INDIRECTLY ARISING OUT OF OR RELATING TO THIS AMENDMENT OR THE TRANSACTIONS CONTEMPLATED BY THIS AMENDMENT. EACH PARTY TO THIS AMENDMENT CERTIFIES AND ACKNOWLEDGES THAT (A) NO REPRESENTATIVE OF ANY OTHER PARTY HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SUCH OTHER PARTY WOULD NOT SEEK TO ENFORCE THE FOREGOING WAIVER IN THE EVENT OF A LEGAL ACTION, (B) SUCH PARTY HAS CONSIDERED AND UNDERSTANDS THE IMPLICATIONS OF THIS WAIVER, (C) SUCH PARTY MAKES THIS WAIVER VOLUNTARILY AND (D) SUCH PARTY HAS BEEN INDUCED TO ENTER INTO THIS AMENDMENT BY, AMONG OTHER THINGS, THE MUTUAL WAIVERS AND CERTIFICATIONS IN THIS SECTION 6.

Section 7. Entire Agreement. The Agreement, as amended hereby, constitutes the full and entire understanding and agreement among the Parties with regard to the subject matter hereof, and supersedes all prior agreements with respect to the subject matter hereof.

Section 8. Severability. If any provision of this Amendment is held invalid or unenforceable by any court of competent jurisdiction, the other provisions of this Amendment shall remain in full force and effect. Any provision of this Amendment held invalid or unenforceable only in part or degree shall remain in full force and effect to the extent not held

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invalid or unenforceable. The Parties further agree to replace such invalid or unenforceable provision of this Amendment with a valid and enforceable provision that will achieve, to the extent possible, the purposes of such invalid or unenforceable provision.

Section 9. Successors and Assigns; No Third Party Beneficiaries. This Amendment shall bind the successors and permitted assigns of the Parties, and inure to the benefit of any successor or permitted assign of any of the parties; provided, however, that no party may assign this Amendment without the prior written consent of the other Parties. No provision of this Amendment is intended to confer any rights, benefits, remedies, obligations, or liabilities hereunder upon any person other than the Parties hereto and their respective successors and assigns.

Section 10. Counterparts. This Amendment may be signed in any number of counterparts, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument. This Amendment shall become effective when each party hereto shall have received a counterpart hereof signed by all of the other parties hereto. Until and unless each party has received a counterpart hereof signed by the other party hereto, this Amendment shall have no effect and no party shall have any right or obligation hereunder (whether by virtue of any other oral or written agreement or other communication). The exchange of a fully executed Amendment (in counterparts or otherwise) by electronic transmission in .PDF format or by facsimile shall be sufficient to bind the parties to the terms and conditions of this Amendment.

(Signature page follows)

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IN WITNESS WHEREOF, the Parties hereto have duly executed and delivered this Amendment as of the date first above written.

[Signature Page to Amendment to Cooperation Agreement]

[Signature Page to Amendment to Cooperation Agreement]