The joys of a BMW auto, and the reason my three-pedaled-challenged wife drives an MB.

I bought an X5 with a known tranny problem and read a lot about them. This is quite common. Some report software updates are beneficial. I changed (no flush, just drain) the fluid and filter on mine at 126k and have (at least thus far) lived to tell about it. Provided you're not really high mileage, I'd start there.