@psrivats if you're making a table, be sure and include Tcase type. Didn't see it in your original list.
Sure would be nice to have a NI data logger, a few accelerometers, and a Dyno. You could spin the various pieces of the drivetrain up to speed and find their natural frequency experimentally. Might give you a clue.
I didn't see in the other thread where we were talking about driveshaft construction. Did anyone find anything out there?
Here is another thought I'm having. The engine, transmission and Tcase are mounted in three locations. They have rubber mounts. So... Not only are you getting vibration, but you're getting enough to overcome the rubber isolation. I wonder what would happen if you added more or less rubber? How about a durometer change? Like try a set of poly motor and tranny mounts.