I don't know if changing the gear ratio will make that much of a difference. The bottom end torque will be reduced and your engine will have to work harder to accelerate at the same rate you do now. Also will probably have to gear down more going up grades. My 4x4 5 speed will cruise up a fairly good hill in 5th gear at 55 mph just by giving a bit more gas. The 2wd automatic always drops out of overdrive to go up a grade unless cruising at 65 mph or so. 2800-3000 rpm seems to give me pretty good fuel economy with the 5 speed