What is the proper gear oil for the differential and transfer case? Any suggestions on brand?

 

Year/make/model?

(I think you have the 3.4, but that is going off memory)

If so, then you want 75 - 90 in the diff, and I believe 80 - 90 in the transfer case. Amsoil is excellent, but any reputable brand will work (Valvoline, Penzoil, etc)

I used Amsoil in the past, but I will be switching to Valvoline because I am swapping diffs and Amsoil is a pain to get.

 

Yeah, I have a 98 4Runner V6.

 

If I remember right, some Auto 4Runners require ATF in the transfer case. But you will need to verify that, I can't remember.

(I really dont think this applies to you)