Ok, I have searched this topic time over. I found threads all the way back to 2008 on this. I am told the "friction" modifier for GTO is NLA from GM and it is now superceded by GM's LS diff lube with the modifier already added. I used this same stuff on my Trailblazer SS as per GM TSB. I have read of peeps using Royal Purple Max and Mobil 1. Anyone out there wanna share their experiences? I also read of using Type F For friction modifier and add that to any diff lubes that don't already have it. Let me know..