Transmission Gear Slipping problems of the 2005 Mercedes Benz ML350

My mercedes ml 350 and ml 320 have both had episodes when the automatic transmission slipped into neutral while driving on the highway. The only common denominator was that the incidents occurred after driving over highway section dividers which were somewhat bumpy. Speeds were approx. 70 mph in all 3 incidents. All 3 times, the car had to be coasted off the highway to a full stop, and shut down. The transmission worked fine after the car was restarted. The ml 320 had 2 incidents in the same trip when it had about 65,000 miles on it. Dealer found no transmission problems. The 350 had one incident when it had 28,000 miles on it, and dealer found no problems.