My job box isn't big at all, but I didn't have a truck to haul it. I know the bigger tires decrease fuel milage, I've had a few lifted trucks. I was just curious if a programmer would help with the towing and fuel milage. I am going to put 4" exhaust strait piped from the down pipe back, cold air intake and a larger turbo mouth piece. I was told by our local diesel performance shop that increasing flow would deffinantly cool it down. I just don't want to spend money on something I don't need to. I am also putting a programmer in it so I can monitor egt's, and maybe bump up fuel economy.