MAKING THE 12 MILE TRIP TO WORK WHEN AT MILE 10 MY TRUCK EXPERIENCED A DECREASE IN POWER FOLLOWED BY A SHUDDERING NOISE WHEN ON THE THROTTLE. LIMPED THE VEHICLE OFF TO THE SHOULDER WHERE I NOTED SMOKE. OPENED THE HOOD TO DISCOVER A SMALL FIRE TOWARD THE REAR OF THE ENGINE COMPARTMENT. TRIED TO EXTINGUISH THE FLAMES WITH NO LUCK AND WITH IN 5 MINS THE FLAMES HAD ENGULFED THE FRONT OF THE TRUCK.