AS I WAS TOPPING THE CURVE OF AN ENTRANCE RAMP, I FELT THE REAR OF THE TRUCK LOSE TRACTION ON THE WET ASPHALT AND THE TAIL STARTED TO MOVE. I LET OFF THE GAS PEDAL TO GAIN CONTROL, AND THE ENGINE CONTINUED TO PROPEL THE TRUCK AS IF THE GAS PEDAL WAS STUCK. THIS CAUSED THE REAR OF THE TRUCK TO CONTINUE AROUND AND SLAMMED THE FRONT OF THE TRUCK INTO A GUARD RAIL AND FINALLY CAME TO A STOP WITH TRUCK PARALLEL TO GUARD RAIL AND FACING IN THE OPPOSITE DIRECTION OF TRAFFIC. I WAS HOLDING THE BRAKES AS SOON AS I REALIZED THE TRUCK WAS OUT OF CONTROL. IF NOT FOR THE GUARD RAIL, MY FAMILY AND I WOULD HAVE BEEN PROPELLED OVER A STEEP EMBANKMENT WITH FATAL RESULTS. THIS IS THE FIRST TIME I'VE HAD THIS OCCUR ON THIS VEHICLE SINCE I PURCHASED IT IN 2001. THIS IS A MAJOR SAFETY ISSUE. *TR