What would cause my car to hesitate only in drive? transmission is fine.

There could be an ignition problem that only exhibits under load. There could be a leak in the air intake ducting that only appears when the engine torques over when under load in drive. There could be other engine control issues but I'd need more information to have any ideas on that. If you want to find a specialist, here's a directory link for you: https://repairpal.com/mercedes-benz-repair-in-hempstead-new-york