So I need to get a new front differential because mine has a crack in it. How do I check to make sure the gearing is the same on the new one so I don't destroy it while putting it into 4x4? Is there any markings or do I have to count teeth?

 

There are two ways:
1. Check the glovebox sticker that has the list of installed options then find a thread on the forum or another that lists the differential ratios...both front and rear will be the same.
2. Take your VIN# and either call Service Department at your local GM Dealer and they can tell you or you can physically go into the dealer and do the same...