I've been asked this question here in the UK, would be interested in your thoughts...

 

The fluid I use has a friction modifier.

 

With a high quality fluid, you should not need any additives. I think I have Amsoil in mine.

 

I try and stay away from additives if possible,

use a good oil with the properties your looking for

Neal

 

Here is my opinion. Based on facts.

NO to additives.
Fact: They can cause slippage and your diff clutch plates to wear out. Or trany plates.

I ONLY use OEM fluids. Full stop.
Why? Well, the facts are that GM gears (trany, difs, transaxles, etc.) can extremely sensitive to fluids, even GM fluids (see how many times the Corvette C7 TSBs changed on trany fluid type as an example, before they found one that actually worked years later).
Those who know, know.

Use only the synthetic GM fluid.
Another fact: It has everything in it that you need, and will keep your expensive gears safe.

Opinion: Royal purple is junk. At least from my experience. Over-hyped.
But, hey, if it works for you, great. Me, I will not touch their oils or greases again.
For example, Royal Purple synth chassis lube separates as the oil runs out, and the stuff left behind turns to a solid lump.
Some of that crap killed my pneumatic lube gun. Something I want in my grease joints? No thanks. GM brand lube from now on.
Hell, you can even see it separating as it oozes oil brand new, just sitting on the store shelf. That is your first clue.

Fact: Using the wrong stuff can be a VERY expensive mistake.

Facts often result in inconvenient truths.

But here is something to ponder. Most auto parts stores will sell you dozens or hundreds of various concoctions to pour into your car, promising everything from extended life, to better gas mileage, to more quiet operation, to more environmental friendliness. Most of the crap does not work as advertised. And who vetted it? Nobody. You know what I am talking about. Caveat emptor.

At least the stuff from GM is vetted by GM.

 

There are a few good additives, LubeGard transmission fluid additive is very good and approved by GM and other OEM's. I put a bottle in every automatic transmission vehicle that I own.
The other is Chevron Techron or BG44k in the tank once a year.