Fluid Change

[WisconsinHick1]

Alright guys I am looking at doing all my fluids in my Denali. I found all the capacities I needed but was wondering about one thing. In the Duramax world I was always told to change the transfer case fluid with the GM Autotrak fluid but have also heard of guys using ATF and 75-90 Gear lube. 75-90 Gear lube seems a little much but is ATF recommended or should I stick with Autotrac?

I will be putting in Amsoil 75-90 in the front and rear diffs.