I have a '85 380SL. The engine was recently replaced. The transmission shifts hard from 1 to 2 and 2 to 3. Shifting occurs at relatively high rpm (~ 4100 rpm).

Can anyone offer guiodance on how to adjust the transmission to provide smoother shifting?

Thank You.

Shifting at 4100 rps is extremely high. to adjust it, under the hood near the firewall follow the throttle linkage. there is a slide adjustment to the Bowden cable. Loosen the screw holding the cable. the proper setting is to lock it in place when you just begin to have tension on it. More relaxed than that and you get shifts under 2000 rpm. More tension and you can control how high the shifts occur.
regarding hard shifts from 1-2 and 2-3, you are not getting proper vacuum to the modulator. Either a vacuum hose is leaking, the seal ring on your vacuum is shot or you just have to adjust the modulator.
It seems to me these issues should have been addressed by whoever installed your new engine
good luck

Vielen Dank!!