my service manual says: for the transfer case use API GL-4 SAE 75w-80, or 75w-90, or 80w-90 it also says NOTE: It is highly recommended to use SAE 75w-90 gear oil.
For the diff. Hypoid gear oil API GL-5 SAE 75w-80, 75w-90, or 80w-90.
NOTE: Hypoid gear oil must be used for differential
It is highly recommended to use 75w-90 visocity.
Hope this is helpful