The 2007 X3 has a major problem with AT shifting and occasional delayed lack of throttle response. I am pretty sure that it is related to the DSC. If your X5 has an off switch like the X3, try turning DSC off and let us know if it improves.
However, it could also be that you have water in your fuel or otherwise have blocked the fuel filter. Try adding a bottle of gas dryer and/or Gumout.