You should not be at 5k rpms constantly. That is so hard on your engine, trans, t case, rear and front end. Sure they can take it for a bit, but I wouldnt be worried about the case. Power comes on its best right around 4200 IMO. I have 4.7s in a truck, single case. Its cool for crawling. If you wanna have momentum, its not the best choice at all, IMO. The distance between gears is sho short, by time you shift it loose stuff, you have lost half your speed. They work fine for crawling and I just use 4th gear when i wanna move, but its still slow.