Hey I know this is off subject I looked up one of your prior post, but it does have to do with synthetic gear fluid.
I have 2016 2500 with the 6.4 not the Cummins. I had a gear swap done to 4.56's. Going to change out fluid after break in this weekend. My ring and pinion shop which is very good put in 75w140 in rear and and 80w90 in front. Im going with 75w90 in front and 75w140 in rear red line from Nick. My shop said absolutely run what I got and not the recommend 75W85. You seem to have more knowledge than me in this,can you give me your thoughts. Thanks.
Brandon: For the front Differential——> If you tow a lot in 4WD or just use your 4WD a lot for extended periods of time? My own recommendation would be RL 75W-110.
If not? RL 75W-90 will work perfectly.
For the rearend: only time I would run 75W-90 is if I never towed & just used the truck as a simple daily driver.
Now if you work the truck? With some towing or a lot of medium/heavy towing I would use either RL 75W-110 or 140 for heavy towing.
Amsoil severe gear is a very Stout/Robust gear oil I would not hesitate to use either but I can get RL cheaper.
You have a good plan: Me personally I would stick with it.
I myself have an idea to use RL 75W-110 / 140 combo in the rear since I will only be towing Only during the summer months.
Maybe with the aftermarket cover (run 3qts 110 & 1qt 140).
Just me thinking out loud. 140 is thick stuff @ 0°F- 32°F.
I only wish I could or have the ambition to install a digital readout thermometer gauge or temperature gauge for the rearend oil that way I could experiment with different viscositys while towing during the summer months that would be kind of cool.
But as for now I can only trust that RL 110\140 will protect my expensive investment while towing during the summer months.
I do have a very nice laser thermometer gun that I can shoot the rearend cover (after towing) to get a decent reading of temperature. I will keep this in the glove box at all time especially during the summer just to keep track of how hot the rearend is getting.
SyN Disclaimer: Remember I pride myself on being different & Thinking way outside the box.
Very few will agree or think as I do. If they do? GOD Help Them!
This post is only my simple thoughts & ideas.