I understand your frustration
I have 2 E53 X5 4.4 my 2004 X5 has 160,000kms and I have had issues with my tranny too. Whenever I come up to say a stop sign and dont come to a complete stop say. I find the tranny is shifting back to 1st gear quick enough, if I get on the accelerator then the tranny does this clunk thing and aggressive shift and then goes. I brought it to a 4th Top Master Mechanic in North America for BMW and he checked and erased adaptive codes that the DME puts into truck and then it ran properly until months later it comes back again. My other X5 a 2002 4.4 with 238,000kms I have absolutely no trouble with tranny.
Did BMW update the software for the tranny? Our trucks are known for tranny issues unfortunately.