FWIW, I'm at least 15K miles with 2 drain bolt changes on the transmission, with the 3rd being a full pan drop/filter change.

Transfer case & diffys were done around 15K miles ago as well.

1st drain bolt was using OEM Esso.
2nd and Pan Drop was using Amsoil ATF.

Amsoil ATF in the TC and Severe Gear 75W-90 in the diffs for me.

The only fluid I had to mess around with was the PS, and I settled in on M1 for this app. The viscosity of the other 2 were slightly lighter and definitely did change steering feel characteristics.