Here is an example of my concern:

I have 4.272 gears in my diffs right now. Changing nothing else, if I upgrade to 4.90 gears in my diffs, my gas mileage has to decrease since my engine will have to do more RPM's to maintain the same speed on the highway that it used to with the 4.272 gears. Can anyone verify this theory??

97 Montero SR w/Mitsu Adj Shocks & Rear Diff Lock ARB Front Diff Lock 4.9 Ring/Pinion 3.15 transfer box 43:1 crawl ratio 2" suspen lift 2" body lift 2" Gas Tank Lift 35x12.5 MTRs 15x10 Wheels Rock Sliderz ARB front bumper w/12k winch Custom rear bumper