In looking at the GMC Service Manual, it looks like this carrier bearing is actually made to slide on the rubber cushion, which is a new one on me. I'm attaching a link which I hope works. Either way, the back shaft and the front shaft each have a slip joint, so if I get a new carrier bearing assembly that is fixed, it ought to do the trick.
In this picture, its the top cut section, manual transmission...
Driveshaft diagram 
