CRUISE CONTROL SET AT 50 MPH, AND AS CAR STARTED INCLINE, ACCELERATOR ENGAGED ABRUPTLY AND RPM INCREASED TO MAXIMUM. MULTIPLE ATTEMPTS TO BRAKE AND REGAIN CONTROL OF VEHICLE. TRUCK WENT OFF ROAD ON CURVE AND HEAD ON COLLISION WITH TREE OCCURRED. DRIVER HAD BOTH FEET ON BRAKE, YET WAS UNSUCCESSFUL IN SLOWING VEHICLE.