new guy with a 1999 yukon slt 4x4

[JQL]

Hello everybody, hope you guys can help me, My 1999 yukon 4x4 slt was making a lot of noise coming from the rear end, I though that it was the transfer case but when I checked the differential It was dry no oil at all and is making a lot of noise from there, the gears look good but my question is this I know I have to replace the bearings but do I have to replace the gears? they don't look bad at all but what do I need to look for just in case am missing something? Thank you everybody for your help .