[elhigh]

Aero drag goes up with the cube of the velocity - double the speed requires eight times as much power. So slowing down even a little can yield significant dividends. 75mph takes about 50% more power than 65! And in a big box like a Trooper it probably sounds like the end of the world.

Try to find a BSFC chart for your engine and shoot for a cruising speed that hits the best power/economy ratio, favoring the slower end of the range (within reason of course).

+1 on the air dam and belly pan/skid plates. Can't possibly hurt. If making a dam fit inside the rig is difficult when you get to the trailhead, look at making it a two piece.