The problem I am having is that under heavy load my truck does not pull like I think it should. The rpm will just level off at around 1500 to 1800. What could be my problem? I replace the fuel filter regularly, and just recently had the lift pump replaced. My truck is an 01 Dodge 2500 "regular" output Cummins. I have the BHAF, Superchip tuner, and 4 inch exhaust. Any information is greaty appreciated.