WHILE HAULING MUCK TO ROCK PICK, OPERATOR NOTICED HIS TRUCK WAS LOSING POWER. EE STOPPED HAUL TRUCK IN SIDE DRIFT TO CHECK AIR FILTER. HE CLIMBED ON LEFT FENDER TO RAISE SIDE HOOD ON ENGINE. H OOD RAISED TO THE VERTICAL POSITION & STAYED. EE CHECKED AIR CLEANER THEN CLIMBED DOWN-HOOD STILL RAISED-W/BOTH FEET ON GROUND-RT HAND AT HIS SIDE-LT HAND ON SIDE OF ENGINE-HOOD CAME DOWN INJ