Royal Purple

I have a 1999 Tahoe, with the G80 rear end (limited slip). I am planning on changing the front and rear diffs to royal purple's max gear oil. I was wondering if i still needed to add the limited slip additive to the rear end with royal purple? from my limited research, i don't think so but i'd like to know for sure. Also, it calls for an 80w-90 oil, but all i could find in royal purple was 75w-90, is this ok? thanks in advance.

No you don't have to add the additive to your diff, it says right on the bottle that it contains the limited slip additive.

Ok thanks... it helps to read the bottle before asking dumb questions. By the way, what kind of benefits should i expect to see with royal purple in the front and rear diffs?

I bought a used car back in 2002 that had a G80 diff. I changed the fluid and used Mobil 1 Synthetic Gear Oil that said it contained the limited slip additive. Within a few days, I noticed a groan coming from the diff when ever backing out of a parking spot or making a tight forward turn. I found some posts on another forum that GM G80 diffs prefered the GM additive over others. I dumped a bottle of the GM lube into the diff and the groan went away.

On the other hand, I did the same thing for my 2000 Yukon with G80 (before I bought the car) and it did fine with the Mobil 1 without the GM additive.

If you notice any noise coming from the rear, you may want to try a little GM additive.

//2000CAYukon