Ive got an 04 2500 six speed cummins and i can hardly get 11 miles to the gallon. 5 in ch exhaust k&n intake. The truck does have a 5 inch lift and 37's. I know that drops the mileage but i didnt think it could drop it that much. I have two programmers a bully dog pup and hypertech. Ive tried them both on the mileage setting and it actually gets worse. Does anyone have any ideas why its so low?

 

is that highway or city?

 

Clean your MAP sensor.......make sure to use an electrical cleaner. Your tires and lift are hurting you.

 

How often do you change your fuel filter? How's your injectors?