Unless it has gotten worse, mine does the same thing. I did have a problem with the first trans in the 250C the wouldn't shift.
Pulled pan, Valve body, every thing looking for a culprit. Nada. Bought a rebuilt one for 500.00. Still in there.
On my 400E when I go from reverse to Drive it hesitates 1-1.5 secs. As far as the manual says, it is normal.
Nature of the beast.