What grade of gear oil should I use for the differentials and transfer case? I hear 75W-90 from some and 75W-85 from others. What do you use and what brand? Also I think we need something that's GL-5, whatever that means.

 

Depends on if you are in warranty and/or are in need of an fluid upgrade due to driving requirements (heavy towing or offroading).

If you fall under the normal duty schedule, any fluid upto spec is fine. Usually they'll run about $15/quart.

If you want kits or upgraded fluid
https://www.blauparts.com/parts/lexu...s/ravenol.html

If your current fluid isnt meeting your needs, a great source of information on fluids is an Amsoil Rep that frequents multiple different toyota and oil forums and recommends the following combo:
https://www.tacomaworld.com/threads/...r-oils.639632/

Hope that helps.