Required maintenance for a 4x4 automatic transmission includes adding an oil cooler, regularly changing the transmission fluid, and changing the oil filter. Overheating isn't as common a problem in manual transmissions as it is in automatic transmissions.
Overheated oil in an automatic 4x4 transmission can lead to premature wear on essential parts, since the parts aren't being properly lubricated. An auxiliary cooler is a good idea for the engine, as well as for the transmission. Even with an oil cooler, overheating is still possible while driving at low speeds, since there isn't an abundance of air flowing over the cooler. The main issue with manual 4x4 transmissions is metal flakes and particles in the oil due to frequent gear shifts.
While draining, it's best to run the oil through fine filter paper or a paper towel to ensure there aren't any particles of metal in the oil. The presence of particles can indicate unnecessary wear or impending transmission failure. If necessary, high-quality oil should be used and replaced in the correct amount.
Additional maintenance for 4x4 vehicles includes paying attention to the transfer case fluid and keeping the differentials properly lubricated with gear oil. All other parts of the vehicle should also be checked for rocks, mud, sticks, dirt and other debris.