WHILE DRIVING VEHICLE JUST SHUT DOWN COMPELETLY. AFTER OWNER TOOK FUEL TANK DOWN, HE FOUND WIRING HARNESS INSIDE FUEL TANK SENDING UNIT WERE GETTING HOT AND MELTED THE INSULATION OFF THE WIRES, AND BURNED THE PLUG. THIS COULD CAUSE AN EXPLOSION. ALL FUSES AND RELAYS WERE FOUND TO BE CORRECT AND OPERATING. PART TO CORRECT THIS PROBLEM HAS BEEN ORDERED. OWNER CALLED GMC, AND GMC TOLD OWNER TO CALL NHTSA.*AK