I have the same problem. One day, Driving back to my home with 60~70mph, I encountered school zone so I braked and kept the 30mph speed, then suddenly the big slamming happened a couple of times, it was like driving over bump without braking, at that time my 2004 x5 has 57500miles on it. after then I felt relatively small shock when I drive 50mph, it was as if brake was applied by itself so felt like pulling back. at that time some electronics made mafunctioning, say telephone red light was always on.

Actually the telephone light was more annoying issue to me. you know it should be gone after start up. so after then I start like this, turn my key into 1 position and wait for a few sec, and then position it into 2 and then again wait for a few sec until the telephone light is gone and then start. and start driving very gently and never speed up but always keep below 70mph . and never have had the same problem so far( for 2months). but really worrying about transmission change.