Car seems to not shift into 3rd when cold

Check the linkage under the stick console. May be lose or broken.

too heavy a motor oil can cause hard shifting also,but when its cold out let your car warm up longer before you take off,it might help

Take off with it in 2nd, and see if you even have 2nd gear. If not, your transmission needs servicing.

This is a computer controlled transmission.If it is making the shifts but they seem to be a little late then most likely is an engine performance issue or a sensor input that is just a little off.need to have a diagnostic run on the car by someone familiar with Mercedes.

i agree that it could be the trans. when operating the vehicle, instead of putting it in drive, put it in 3rd. accelerate to 40-50. the vibration might be the result of the trans not being able to shift properly into overdrive (4th). if the vibration goes away, then suspect the trans, since the trans will no longer be able to shift into 4th. if the vibration is still there, suspect an axle out of balance since the speed of the axle will remain the same.

scap it

have you checked all trans linkage for proper adjustment?

Yes you need to have it adjusted.

Not sure on yours but on my vehicle, it doesn't shift up until engine reaches a certain temerature, and right now in the winter weather it takes a little longer. On mine it's normal.

I own a 1995 Ford Probe SE 2.0L that suffered the same problem. The transmission shop Techs insisted the transmission was blown and needed replaced. After doing some research it turn out to be the Park Neutral Switch also known as a Transmission Range Sensor right below the air box. The part cost 54 bucks. The problem stopped after replacing it. About a year latter the problem came back. After doing some more research it turn out to be the VSS speed sensor. The part cost 57 bucks. The problem stopped after replacing it.