I had a Hemi, with 4.56 gears. It got 12 mpg normal driving. Towing 5000 lbs, it got 8.5mpg. The programmer will help you some, maybe 1 0r 2 mpg. If you change gears to help it get up to speed you will hurt the mpg. Because when you are cruising the motor will be turning a higher RPM. You spend...