RE: Overdrive unit for a 4x4?
Yes there are units for our trucks. Gear Vendors is one, and US Gear is the other. One of them goes after the transfer case, and then only enguages in 2 wheel drive. The units are rated at very high HP and toque limits as well as towing capacity. They are both very expensive and it is doubtfull that you would see a R.O.I. unless you drive alot of miles and keep the truck a long time.