AZ Diff got me in on a Saturday morning and it was done by noon. Changing the gears made a huge improvement, but I may now be going 4.10's. It was suggested that I go 4.10's in the first place and now I know why. No matter what you go with you will love the feel. Good luck!
If you have a 99-up I would definitely go with 4.10's! The rpm difference is minimal to a 3.73 and the feel is way better. But that's just me but if your going to put your car on the track then 4.10's all the way.