When my engine mounts went I felt it both in P and in D. As it got worse I heard more than felt it at high speed it sounded like a low drone.
The thing is sometimes the engine mounts do not fail all at same time so your vibration may be sporadic. If you can get under there you can probably tell which engine mount is bad by how thin and squashed it actually looks and how close the engine metal is to the frame.
Just a little info for you hope it helps...
88 230E (W124)