my 02 2500 4x4 long bed with 4"exhaust(planing to get 6" dual stacks)with about 154,000 miles with kn cai,and my truck has 245/75 r16 (had 285/75) now im getting around 19-22 mpg. at 65 mph do you used a fuel treatment like lucas you might want to changed your fuel filter every 30,000 miles that...