The GV may shift at lower speed, but that doesn't mean you *should*. The GV system uses a hydraulically shifted spring return movable cone clutch, with the hydraulic pressure provided by an input shaft driven pump. Obviously the faster you're driving the more volume the pump puts out, and below a certain speed it woln't put out enough volume to build pressure properly. Likewise, the lower speed means less volume which means slower shifting. The long and short of this is that it may *shift*, but that doesn't mean the pressure isn't too low to fully apply the clutch, with the result that it may be slipping, and likewise the shift may be slower than optimal leading to more slippage ie wear. With as expensive as the clutch is I wouldn't risk it.
The US Gear/Doug Nash does not go between the engine & trans, it goes aft of the trans but before a t-case if on a 4wd.
My $0.02 is that both units could fail and strand you. It sounds to me as if most failures on the DNE/US Gear are electrical - failed shift motors/control which will almost certainly not strand you. The only way I could see it would is if it fails mid shift which would be highly unlikely, and even so could be fairly easily overcome by removing the motor or side cover and rotating the screw by hand.
Total mechanical failure would strand you in either case but it seems unlikely. The DNE/US Gear is a quad contershaft design and while it does seem to have weak thrust bearings, you'd have to do some serious damage to totally destroy it. Even a bearing failure or similar I think would leave enough intact that it could be driven, apt slowly and noisily.
Wear parts for the US Gear/DNE seem pretty easy to get. I've located sources for about half the bearings (including the commonly failed thrust bearings), both seals, shift motor & switch for reasonable prices. I'm fairly confident that the sliding shift collar and fork are common manual trans parts and could be found with a bit of research and the proper catalogs, and I'm 95% confident that the remaining bearings could be easily found. About the only parts I'd expect to be irreplaceable are the gearset, shafting & case. Same is true of pretty much any trans though, and none of those are really wear items.
My parts/info thread:
http://www.oilburners.net/forums/showthread.php?65234-US-Gear-Dual-Range-Doug-Nash-Info
Theres no way to safely drive hwy speeds here when it snows. My truck and jeep are literly all over the road and unsafe at faster speeds. They even close the schools when it snows 1/2 inch because the school busses get stuck at bus stops or end up in a ditch.
Keep in mind it's very flat here, mountain grades would give me a whole new perspective.
even when snow is just forecasted, doesn't even have to be on the ground yet.
