Before there's any misinformation spread, I've had a US Gear Overdrive on my 2001 ETH 6-speed 4x4 since December.
The thing works flawlessly. The shifting action is clunky (literally), but once you get used to it, it's not a big deal. You really learn to appreciate having twelve gears to choose from when you're winding up a twisty mountain road carrying a load, and like to keep the RPMs right at 1800-2200 so your EGTs stay sane (as the altitude slowly climbs from sea level to over 7000').
So, to reiterate... they may only now have an adapter kit for the 4x2's, but they've had a 4x4 application for a good while now.
Rob
The thing works flawlessly. The shifting action is clunky (literally), but once you get used to it, it's not a big deal. You really learn to appreciate having twelve gears to choose from when you're winding up a twisty mountain road carrying a load, and like to keep the RPMs right at 1800-2200 so your EGTs stay sane (as the altitude slowly climbs from sea level to over 7000').

So, to reiterate... they may only now have an adapter kit for the 4x2's, but they've had a 4x4 application for a good while now.
Rob