Synthetic Gear Lube

[bbt8831]

I have a 98 Tahoe LT 4dr 4wd. My question is if I change the lube in the rear end to royal purple, do I still need to add the posi trac additive stuff? Truthfully I don't even know if the rear end has a locker at all but it is the only vehicle here right now so if I find it has one once the case is opened it will be too late to run to the parts store/dealer. Anyway just trying to make sure I have what I need on hand before I get started. If anyone knows the build code for I could check the glove box tag too. I think my 88 had something like GU6 OR GU4 for an open diff 3:42 anyway thanks in advance for any help...Brian

 

[SunlitComet]

if oem stock with a locker DO NOT USE a additive.

 

[msark]

I had used Lucas with additive but it was noisy... Flushed within 50 miles and put in Amsoil without additive... Was instantly quieter .... Hope it helps the longevity issues these rear ends have ....