Drive shaft play

Lately I have been noticing a vibration driving my truck between 45 and 65. Figured it was U joints so I jacked the back of the truck up put it in neutral and got under it to check them. I found out that the back u joint is bad and I also noticed where the drive shaft goes into the transfer case has some play. When i was at advance auto parts getting the u joints there is a transfer case shaft bearing that shows up in the computer. Is this something that comonly goes bad and i have to change it? If so how big of a project is it to change?I have had a couple people tell me that is normal and not to worry about it but I figured I would ask on here and maybe someone would know more about it.