I WAS DRIVING ON HIGHWAY WHEN I NOTICED SEVERAL PEOPLE PASSING ME ON THE RIGHT AND POINTING DOWN AT MY TRUCK. I REMEMBER MY TRUCK HAD SLOWED DOWN AND WHEN I WENT TO PRESS ON THE GAS AND MOVE TO THE RIGHT LANE TO PULL OVER IT DID NOT RESPOND. I THEN NOTICED SMOKE FILLING THE CABIN THAT WAS COMING FROM UNDERNEATH AND UP THROUGH THE TRANSMISSION STICK. WHEN I HIT THE BRAKES THEY WENT RIGHT TO THE FLOOR. I ENDED UP USING THE EBRAKE TO SLOW THE TRUCK DOWN AND PULL TO THE SIDE. WHEN I EXITED THE VEHICLE IT WAS ALREADY ON FIRE AND I PROCEEDED TO MOVE MYSELF TO SAFETY. A PASSING FIREMAN TRIED TO USE AN EXTINGUISHER TO PUT OUT THE FIRE TO NO AVAIL. THE TRUCK ONLY HAD 14000 MILES ON IT AND WAS TWO YEARS OLD WITH NO RECENT WORK DONE TO IT AT ALL