I'd take it back to the dealer and have it looked at. FWIW, I always control the shift points by hand with the lever, as the MB trannies are a little eager to upshift at part-throttle IMO. All in the name of fuel economy, I suppose.
Oh, a lot of people have been VERY happy with Mobil-1 synthetic ATF in place of the usual dino fluid. Don't know if that would help your problem or not. I'm assuming the 60k service included a trans fluid & filter change, of course...