Transmission Slip Out Of Gear problems of the 2012 Mercedes Benz GL450

After purchasing the vehicle used from a dealer (with @ 36,000 miles) I started having transmission problems within a year. When I would be stopped on a hill/incline and then accelerate the car would violently jerk (as if I had hit something). It would not go forward until after the sudden jerking motion stopped. It would also behave this way when I backed up a hill or incline. Every year I brought it to the dealer to diagnose and fix it and they told me that they couldn't reproduce it when they had the car, therefore they couldn't find out the problem. I also told them that the engine light would come on and off intermittently, however, they were unable to figure out the problem. Every time I took it in for a service they documented the problem on the estimate sheet. However, this last time I brought it in they were able to diagnose the problem as a faulty transmission. It would slip out of gear when on a hill or slight incline when put into drive or revers from a complete stop. Come to find out when researching these cars that mercedes have had this problem with their engines for a long time.