We have a '05 Suburban with 215k miles that has done a good job towing our travel trailer. When we bought it used in '13, I swapped the transmission fluid out to Mobil 1 ATF. And also the rear axle to Mobil 1 75W-90. Those 40k miles went trouble free for the tranny and axle.

We recently bought a '15 Suburban to replace the '05 and I want to do the same thing to the newer one. But now the tranny fluid is Dexron VI and the Mobil 1 isn't spec'd for that. Valvoline fully synthetic and, of course, the Dexron VI fully synthetic pop up as certified for this tranny. Any other options? Which of those two would you use?

And on the rear axle, the owner's manual gives a AC Delco 75W-85 synthetic fluid along with the GM part number. That part number shows up as a bottle that doesn't show synthetic on it. Would you run the Mobil 1 75W-90, or something else?

I'm long out of warranty, so that's not an issue.

Thanks.

 

use what the manual specifies

 

Run dexron 6 in it. It is synthetic. The valvoline dexron 6 in the blue container should be fine. I believe rear axle is 75w90. I like lucas 75w90. Front is 85W90 I think If I remember right. It should be in your owners manual.

 

Thanks. I found out after my post that all Dex VI is fully synthetic. Rear axle is 75W-85. The confusing thing about that is the manual specs 75W-85 synthetic, and gives a GM part number. When I look up that part, a picture of the bottle doesn't say synthetic. I need to investigate this more.

 

"synthetic" is just a marketing buzzword with no basis in reality or regulation.
All that should matter to you is that the fluid meets the ASTM performance specifications in the manual.