Fourtreks is a distributor for the Klune-V Extreme Underdrive.  It is planetary gear box that goes between your transmission and transfer case and comes in two different ratios.  The David 4:1 and the Goliath 2.72:1.  This gear box can be adapted to go between many transmission and transfer cases out on the market.  Chevy, Ford, Jeep, Dodge and Toyota.  You can also mix match transmission and t-case types by mounting a Klune -V underdrive between them.  As an example you can use Turbo 400 Chevy automatic, Klune-V 4:1 and Ford NP 205 combination in your vehicle.  One of the advantages of using a Klune-V underdrive is that you can keep the low range that  comes stock in your vehicle's transfer case while adding a whole other lower low range which can be doubled up with your transfer case's low range.  Also, Klune-V gear boxes have a long track record of durability.