I think its FIXED! I reinstalled the rear driveshaft rotated 180 degrees and the vibration is almost completely gone. I mean 100% better! Since this is my first D90 and its vibrated since day 1 I'm not sure what the optimum experience should be. Here is the theory of what happened:
We replaced the u-joints first as a possible fix but more as a maintence measure as this is a new vehicle. At the same time, the front left wheel bearing was in desperate need of an adjustment/repack as there was significant play . We think that during the u-joint replacement, which we did first, the shaft was mistakenly reinstalled 180 degrees off. So at one pont we had the wheel bearing AND the rear shaft causing vibration. When the wheel bearing was fixed we did not think to consider the rear shaft because we assumed the u-joint/install was correct. So the wheel bearing gets adjusted but the rear shaft was off.
This was a great learning experinece for me and a lot of really good posts on this thread to help other folks troubleshoot the driveline.