i put a cummins out of a bus in my 4-door duelly truck.have a 4-speed manual trans with a gear-vender over/under aux box and 3;55 gears.towing my trailer with 2700 lb. car on it i get 25mpg running 80mph on cruise..wouldn't go any other way for towing..converting from a 454bbc[gas]to the cummins was a cake walk.