Normal automatic transmissions in gasoline engines shift via the vacuum produced by the gasoline engine, but the automatics on diesel engines need to have vacuum produced by a separate vacuum pump.
After that having been said, it isn't unusual to have to manually shift one of these transmissions, or to have them need to be kicked down on hills by "flooring it".
Y'all ain't the Lone Rangers heah, it's just the nature of the beast! And john, I'd take that transmission problem to a reputable Independent garage, or even to AAMCO before I had the dealer gouge my wallet out of my pants. After all, transmissions are transmissions, even in a mystical Mercedes...
Perhaps all your problems are vacuum related, and not transmission problems, but I would still suggest a fluid and filter change before you see varnish or discoloration in the fluid... And consider Redline
http://www.redlineoil.com, or another synthetic fluid when you do change the fluid.