Help me pick a Diff Fluid, 23 GMC Sierra 1500 AT4

[BobsArmory]

Looking to swap out the factory fluid in my trucks front and rear diffs.

2023 GMC Sierra 1500 AT4 3 liter Duramax
Factory Specs
Front: 75W-85 Dexron Low Viscosity ACDelco part #10-4122
Rear: 75W-85 High Efficiency Synth Hypoid Gear ACDelco part #10-4091

I was thinking of using something like 75W-90 Amsoil Severe Gear or HPL Differential Life 75W-90 but was wondering why they specify 2 different fluids. One has a friction modifier and the other doesn't? GL4 and GL5?

What are your thoughts?

 

[Bighorn2500]

Looking to swap out the factory fluid in my trucks front and rear diffs.

2023 GMC Sierra 1500 AT4 3 liter Duramax
Factory Specs
Front: 75W-85 Dexron Low Viscosity ACDelco part #10-4122
Rear: 75W-85 High Efficiency Synth Hypoid Gear ACDelco part #10-4091

I was thinking of using something like 75W-90 Amsoil Severe Gear or HPL Differential Life 75W-90 but was wondering why they specify 2 different fluids. One has a friction modifier and the other doesn't? GL4 and GL5?

What are your thoughts?

Does the rear have a limited slip differential? Typically LSD’s get the friction modifier.

Either of your choices are both very good options.

 

[BobsArmory]

Does the rear have a limited slip differential? Typically LSD’s get the friction modifier.

Either of your choices are both very good options.

It does have a locking rear diff.. As I recall it has an Eaton Locker but I cannot be sure at this time.

 

[mr_boring]

I know people will disagree, but if you are just driving it, use whatever. If you tow often or heavy, use a heavier weight. You can't go wrong with either of the ones you are looking at. I use Valvoline 75/140 because it's inexpensive and I love the flex fill packs (which Amsoil probably invented). I very rarely tow but old habits die hard.

 

[BrendanC]

HPL differential life 75w-90
amsoil severe gear
any syn off the shelf gear oils

^^^my order in picking differential oil. my uncle runs a fleet of tractor trailers and tractor trailer wreckers and he swears by the Amsoil severe gear so i rate the HPL and amsoil very close.