Hi,
As I promised to you yesterday, I am back with the solution. Since my car had the same problem, I brought it to a MB service. The reason is a faulty Speed Sensor on the rear axle. Due to the fault, the computer does not allow the gearbox to shift into higher gears. The labor, part and taxes (I live in California) are $376.00. Surely the best if you can find a MB shop (not necessarily a dealer) to take care of it. In case you don't have independent MB repair station bring it to a dealer's shop. Please note that the computer is going to read the problem correctly when the car is in the faulted (several warning lights are on) mode!! Good luck,
Paul