WHILE ENTERING INTERSTATE I-10, EARLY MORNING TRAFFIC. TRAFFIC MOVING AT 20 - 25 MPH. ENGINE MADE A SERIES OF REVVING NOISES. TRIED TO APPLY BREAKS TO MERGE OVER. BREAK PEDDLE WOULD NOT ACTIVATE. STUCK IN UP POSITION. I APPLIED BOTH FEET AND PRESSED FULL PRESSURE. WOULD NOT GO DOWN. WOULD NOT STOP. ROLLED INTO THE BACK OF THE VEHICLE IN FRONT OF ME. FORTUNATELY I WAS ONLY MOVING ABOUT 20 MPH AND NO ONE WAS HURT. I WOULD NOT DRIVE THE TRUCK AND HAD IT TOWED. DEALER NOT ABLE TO DETERMINE ISSUE.