Strangely enough, 2nd gear is really the only gear with sufficient torque to cause the vibration, but the vibration can be felt on decel with the car in neutral from 30-20.

Update though, and a little progress;
I dropped the car off at my indy today so he could shed some light on the situation. He claims that I'm missing the shim, or bracket, under the trans mount between the cross member. I read about this elusive shim before and was very diligent to *not* lose the magic shim. But there was nothing. No bracket, just a trans mount when I dropped the cross member. My indy shimmed the mount and said the vibration is greatly reduced.

So now what? "Greatly reduced" wasn't what I'm after, its a Mercedes and it should feel like one.

Also, what is the correct orientation of the CSB and carrier? I made sure to put everything back together as it came apart but I'd like some clarification to ensure that I'm not going down the wrong rabbit hole.