I think the X5s are having the same issue as X3s of same model year. There is a sticky in X3 forum for the "hesitation" you guys here experience. A temporary fix (on X3) has been to put the key in position 2 (do not start the car) press the gas pedal all the way down and keep it there for 40 seconds. This puts the transmission in learning mode again and the car behaves good for few days/weeks. Unfortunately its just temporary. The permanent-in-some-cases fix has been a s/w update. This too does not work in all cases. Good luck.
(OO \ (|||) (|||) / OO)