This topic has been dealt with over the years fairly comprehensively but there is one issue I didn't see resolved. The cruise control built into the ECU checks engine RPM against speed. This is really only relevant to 5th gear. If the engine RPM is lower than it should be cruise control will not engage. With the standard 1.41:1 transfer case ratio obviously everything is fine, but when you change the ratio to 1.22:1 as I have the vehicle ECU won't activate cruise in 5th gear as the engine is only doing 85% of the RPM it should be. The answer to this is quite simple. A Dakota Digital SGI-5 interface (for about $140 landed) fitted between the Speedo and the ECU lets you calibrate what the ECU receives but still leaves the speedo reading correctly. Works a treat.
Hope this is useful info.