Some of these are guesses, but going though as many window stickers as i could find, these are the fuel economy figures for the 18 expy and navi.
Exp SWB 2WD: 17city 24 hwy
Nav SWB 2WD: 16city 23hwy
Exp LWB 2WD: 17city 23 hwy
Nav LWB 2WD: 16city 22hwy
Exp SWB 4WD: 16city 22 hwy
Nav SWB 4WD: 16city 22 hwy
Exp LWB 4WD: 16city 21hwy
Nav LWB 4WD: 16city 21hwy
Exp SWB 2WD: 17city 24 hwy
Nav SWB 2WD: 16city 23hwy
Exp LWB 2WD: 17city 23 hwy
Nav LWB 2WD: 16city 22hwy
Exp SWB 4WD: 16city 22 hwy
Nav SWB 4WD: 16city 22 hwy
Exp LWB 4WD: 16city 21hwy
Nav LWB 4WD: 16city 21hwy