You need to have a MB shop or tranny shop ck the vacuum at the actuator to see if it is in spec. You also need a test done for the pressures on the tranny. Most times when a tranny shifts ok in the first couple of gears and flares up in 2 or 3 the tranny is probably on its last leg. You can try to service the tranny but usually makes it worse . I would recommend having a shop look at this problem.