I just replaced my center support , with new bearing on my 94 e320 with, your exact symptoms, vibration at full throttle in 1st gear gear, and rise in vibration the faster i went, i had vibration felt in seat, although wife didnt
know anything was wrong , bearing is loosely pressed into driveshaft, i used a press to remove old bearing , was easy to do, i also had a whine that i thought was transmission , after replacemnt whine is gone, smooth as butter once again,my center support rubber was broken all the way around, and i have 191k miles