intermittent automatic trans problem

My 2005 Buick Le sabre sometimes does a "jerk" when accelerating from stop.
  Manual shifting to # 1 ( low ) position prevents this from happening. No codes are set on the CPU .  After the occasional jerk, all shifting, including downshift work great.  Four different trans repair shops are unable to diagnose the problem.  The car has 90, 000 miles on the odometer. Trans has proper amount of fluid.  This has been happening about 7 months, a few weeks after I purchased the car with 74,500 miles on odometer. This jerk has happened as much as 12 times during a 50 mile trip and no jerk for as much as 3 - 4 weeks time.  If accelerating very very slow from stop it does not jerk.     Last fall it was driven on a 1150 mile round trip vacation and only jerked  3 ( three ) times.  Am I the only Buick owner to have ever had this strange problem ?
thanks: Ted P.