Today we are servicing the front and rear diffs and transfer case on my 2021 Ram 1500 4x4.
Service intervals for the differentials is 30k miles and 40k miles for the transfer case.
This is a relatively simple inexpensive service requirement. The differentials take standard gear oil. Just research your vehicle to be sure what weight is recommended for each axles and if limited slip additive is needed. Mine called for 75W-90 in the rear with limited slip additive and 80w-90 in the front. 75w-90 should work fine in the front as well. 4qts will be enough to do both.
The transfer case is an easy procedure as well, but these Rams have a transfer case that requires special fluid from Mopar. In my case I have a Borg-Warner 44 and the fluid it requires is 40+ dollars a quart and requires 2 quarts. Definitely alot more than most that use standard ATF fluid.