I think this too is a great idea! A handful of G8 owners have replaced their full diff assemblies with the Camaro ones (it fits apparently).
Having a GXP I already have a 3.70 rear-end but I wonder if the 3.91 would make a noticeable difference??? Anyone moved up .21 or so care to comment?
Also, why not go with the supposedly better 4.11 from Richmond instead of the 4.10?
2009 GXP, Manual with Sunroof
Zeta platform, LS3,TR6060 tranny ... ya, it's a 4-dr Camaro!
Borla cat-back, H&R springs, & Sprintbooster & I love it!