I have a 2007 X5 E70 4.8L with 133K that I had the...

I have a 2007 X5 E70 4.8L with 133K that I had the propeller shaft and the flex disk replaced due to the deterioration of the of the universal joint. I do have the old part and there is play in the universal joint. When the car came back I had a vibration that shook the entire car like an out of balance tire. I had the tires balanced, no change. I took the car back and was told that the propeller shaft was not the issue. But the transfer case required replacement. The vibration happens only after the car is driven for 20 to 30 minutes (well warmed up) and under moderate to hard acceleration. There is little to no vibration at cruise or deceleration. The vibration was not present before the propeller shaft was replaced. I asked them to check the center support barring which they say is not damaged. Due the sudden onset of this problem not accompanied by any warning lights, plus my past experience with this BMW service center who recommends parts replacement for every issue plus the cost of the transfer case I am questioning their diagnosis. While requesting your opinion as well as alternative thinking on this issue.