Bentley's after-market Service Manual for the X5 says that out-of-balance at 60 mph, particularly under braking, is most likely caused by loose bushings and ball-joints in the suspension linkage, than by warped rotors, etc. If you've balanced the tires three times by three different shops, the balance is NOT the problem. Jack the front wheels off the ground (support it securely w/ jackstands), and have someone shake the wheels while you lie under the car, and feel each of the four linkage arm ends, in turn. There are two bushings at the chassis end of the links, and ball joints at the wheel ends. Total 8, two bushings and two ball joints on each side. On my car, three of the four had noticeable play, on each side. Replaced them and the problem went away. Just got back from towing my motorcycle on a trailer from south Florida to Lake George, NY, 3000 miles total, NO PROBLEM! Forget about the balance - get under the car, and check the bushings and ball joints! (Insanity is defined as repeating the same actions, and expecting a different outcome.)