Geezzz.. it sounds like have analyzed the crap out things! After all that I would be really frustrated! I hate vibrations!
So you know when you remove the rear drive shaft, and drive with the front axles engaged, 4-wheel high, you will get some interesting "power steer". That would be the next step that I would do to see if it eliminates the rear drive shaft. That may not necessarily eliminate the rear diff, ring & pinion?
Gnarls.
