The shifting on this car is controlled by vacuum rather than a computer. The firmness of shifting can be adjusted assuming that there are no vacuum leaks.

On the side of the transmission is a device called a vacuum modulator. This can be adjusted to soften or firm up shifting. The key is not to overdo it so that the transmission *flares* when it shifts.

Take it to a knowledgeable Mercedes service facility and have it looked at. It CAN be corrected if things are otherwise operating normally.