I did everything I knew to get good fuel economy out of the 1990 Cummins Dodge. Larger pipe, overdrive unit, 3:08 final drive ratio, low rolling resistance Michelins, replaced tail gate with net. Got 20 mpg going up there through W. VA (I-77 then I-78). Only got 14 mpg on the way back pulling the load (I-95 & I-85). Trailer was 2,200#, so about 3 tons total. The cruise control didn't have the suds to pull the throttle very hard. But the truck did a good job. Little things to fix.
Windshield wiper linkage popped loose, A/C needed some freon, glove box door latch broke (now has binder clip), drivers door panel came loose.
It was fun!