Why is it that everyone thinks there is some little trick that will "Magically" improve their fuel economy for next to nothing ?
I was in the business and know that engineers would give their left gonad for 10% better fuel economy !
The 4.0L just gets bad fuel economy, period.
Synthetic oil helps some. Change to synthetic in the transmission and rear axle also helps.
Better air flow (holes in the air box or a whole K&N cold air intake kit) helps some.
Everything I mentioned might get you 2-4%. | 
