OK guys, I Found the solution !
After some more testing, I found out, when switching the display to the VSD Mode, the stuttering starts, and when switching back to normal MAP Mode it is smooth again.
FS2Crew automatically switches the VSD on, when calling the "RWY ENTRY PROCEDURE", and therefore the stuttering begun.
So now after this, I am Not longer sure, if it really is FS2Crew related or more a PMDG problem.
Hopefully this Information can help you with your stuttering.
Regards
Frank