I have a US Gear unit in my truck. I chose the underdrive because I do most of my pulling in the mountains of NC. I have the 3:54 gears. I am thinking very seriously about spending the $500 to turn the gears around in the unit and go overdrive. Love the ability to split gears, keeping the engine right in the power band at all times. I don't like the shock to the drive train when shifting, if you "don't get it right". The unit has been in my truck 35,000 miles with no problems.
------------------
97,ext cab,4x4,5spd,US Gear box.