A couple years ago at 82k miles I changed my ATF to AMSOIL Signature Series ATF and changed the filter.
AMSOIL Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid
I did an initial fill and then changed the fluid 4X running about 20 miles between each drain and fill. Each drain and fill took about 4 qts. In this way, I got the entire system flushed with good fluid, minimizing or eliminating the old fluid residual rolling around in the converter and other places. A total fill is listed as 10.2 qts, so despite my perhaps overkill, I'm certain that I got to an all new fluid.
At 96K miles now with no complaints with a recent 1200 mile 4,000# trailer pull under my belt.
Updating my previous post: I am at 100,000 miles and continue to experience smooth operation.
Used the same ATF in the Xfer case as well.
For the Front and rear Diffs I used this:
AMSOIL Severe GearŪ 75W-90
These AMSOIL products have always delivered for me for over 25 years.
Despite this, I did recently change to Shell Rotella T6 for my engine oil as I felt I was no longer using the AMSOIl to its fullest 25,000 mile potential and the Rotella T6 oil analysis shows to have as nearly a high TBN number as the AMSOIL.
and lower cost.
Mike