How long has this been going on? Did you do any work then the vibration appeared.
How is your timing, what is your base timing set at? Is the timing (mark) jumping around at idle in gear?
Motor mounts? Transmission mount? Take the transmission tailshaft and try to move it- if it moved your trans mount is bad. and the tans is sitting on the crossmember. Does it do it when you are turning
since it does it in park, its not the driveshaft. I would be surprised if its the tc too.
