I called RL at one point because I have a lot of Shockproof left over from motocross days. The light version is the stuff for separate gearboxes like in the older 2 strokes. They recommended against Shockproof in my F250 differential, saying that their 75w140 lube is what they choose for Ford LS diffs. Now, YMMV for the GM you mention. Call them up.. they are pretty nice guys and are usually willing to talk about their products. BTW, I went with RP Maxgear just because of availability. No issues, no complaints so far.
