`95 3500 TRUCK HAS TONS OF POWER ,BUT WHEN TAKING OFF,OR IDLING FOR A BIT AND TAKING OFF. IT REALLY BELTS OUT BLACK SMOKE. . JUST BOUGHT TRUCK. DO NOT KNOW WHEN VALVES HAVE BEEN ADJUSTED. MILEAGE IS ALSO POOR. 15MPG EMPTY,WITH 3. 54`S AND STICK. RIG HAS NO MODS. ANY IDEAS ??