After 80K+ miles of abuse, my U. S. Gear dual-range auxiliary transmission finally broke... well not really broke, just that it wouldn't down-shift, leaving me in O/D. I finally got it into straight drive and left it there. I called the company in Illinois and they gave me instructions on how to check things out as they thought it was the motor that winds the spring that... well, you get the idea. It sounded like more than I wanted to do in the triple digit heat of Havasu :--) and got a dealer in Phoenix (Chuck's Speed and RV Center) to do the work.
It was the motor and all is well now and the guts showed no signs of my abuse... these things are as close to "bulletproof" as are made. I inquired about the Gear Vendors compared to the US Gear unit and was told that the Gv unit can be shifted directly up or down without "blipping" the throttle (on ATs only) but besides not being compatible with use in 4WD, are to be disabled on the downhill. US Gear does shift hard enough to remove doubt that it is gear :-laf but can be used on the downhill with an E-brake with no sweat. I know as I have been using mine that way for years. It does require clutching or a throttle blip to shift. Each usually results in a manly thud as it shifts. 

