Update - I'm taking my truck into a different Chevy dealer service department tomorrow morning, to have the drivers seat movement issue fixed, under one of the existing TSB's out there (#13310A, PI1183A, or 15304). The service manager I talked with seems like a pretty knowledgeable guy, and ordered the parts for the movement issue beforehand, so they won't be waiting on anything when my truck arrives.
I'm also going to have him check the torque on my u-bolts, to be sure they're at the correct factory tightness of 78ft.-lb. We'll see if it will help the "clunking" in the read-end when I'm coasting, and then re-apply the gas. He's also going to check that all of the factory updates for the transfer case have been applied. If nothing else, at least this will be the 2nd service visit on record for the rear-end "clunking" issue.
I'll report back in, once I've picked-up my truck. Happy New Year All - Rick