I have found a lot of the mpg is in the trans. Also with a mechanical injection pump if you can fuel hard at a low rpm to spool the turbo you're into power quickly and don't need to keep your foot in it (poor mpg) personally I go crazy driving my father's duramax or newer common rail Cummins, even though both have 150hp tunes they feel sluggish down low compared to mine or my brother's 12v trucks. We both run some pretty built autos and nice converters both with 3.54 gears and 4x4 trucks. They're fun when the cars are down or 4wd drifting in winter lol