you may want to visit
http://forums.trailvoy.com/. i have an 03 envoy 4x4 that i wanted to lift. but they say that if you want anything more than 2" that you'd have to straight axle the front. this is because on envoys and tb's they use a type of driveshaft like a front wheel drive car. the pics i have seen of them lifted higher then 2" were photoshoped.