I use Red Line in everything EXCEPT the Tranny. Both Red Line and Mr. Goodwrench at the dealership said it would not be a warrenty problem...but from the posts I've been reading, it seems like any change in anything could be challenged by GM, if it ever came to that. For me, I'm going for it. Red Line is superior to Mobile One and other stock fluids. My Uncle Jim in Illinois uses it in his race car and told me they tested the rear axel temp before and after Red Line and found that the temp. was 50 degrees lower with Red Line. He also got another 35 degree reduction with a product called "ER"(Energy Release). You can do a search on Energy Release and find their website. A lot of racers use it.
I use both products. I had a problem with some gear grinding in my tranny that was progressing. We flushed out the Red Line and ER, and went back to stock Chevy ATF, and the problem fixed itself. Mr Goodwrench said the Red Line was the problem, but I think the ER is just too slippery for the clutches.
FWIW, that's my experience. BTW, Red Line claims you'll pick up a couple of ponies in your engine and offer better protection than Mobile One. So, why not use it? It's $8.00 per quart.....Good Luck /phpBB/images/smiles/icon_smile.gif