For the sake of number comparison, my setup:
'92 XJ, Stock 4.0l HO, 3.07gears, 5sp, 3" bastard pack lift, 31x10.5 Grabber AT2s, non-corrected speedo (even tho GPS says it's spot on...) with ~250K mi. I get 15mpg city, 17-18,mpg hwy. If the ambient temp is over 80*F for the duration of a whole...