How bad are the vibrations? Are you seeing any fluctuations in the RPMs? Any lose in the MPG you where getting before? Any other drivability issue, even if they are small? Anything you can give will help narrow the search. Right now it would be a pretty big list if I wrote it out.
That could very much do it. When the car is cold, start it up and put your hand on the tranmission mount and see if that is the bulk of the vibration. Regardless, fixing that is likely a good thing, but it's going to be a pain to replace.