First post here. Long story short, I've been following this thread for about 6 months, as I've got a shaker. Dealer does the usual, tires tires tires. Today I removed the rear drive shaft, put a bag over the transfer case output to catch most of the fluid that I knew it would sling, drove a couple of miles at the worst speeds for my vibration (45 and 65), and observed the vibration to be completely absent with the rear drive shaft removed.
I just finished refilling my transfer case, and am now thinking about where to go next with what I'm telling the dealer. I'm thinking it might be related to pinion angle.