STG1BUICK

Bought our 2005 V April 2010 and it came with a full warranty that ran out January 21 2011. Just before it went out, the pinion bearing started making noise and the pinion seal was leaking along with the slave cylinder. The dealer replaced the entire differential and the slave/throw out bearing. It came home with a tip in vibration at 50mph and up. The dealer listened to it and told me they were no longer a Cadillac dealer (they lost their franchise in October but didn't tell me when I took the car in for service) and I would have to take it to another dealer, now out of warranty. Cadillac had me take it to another dealer and they put another differential in and indexed the drive shaft. They then rebalanced all the tires. Now they say the car is as good as it can be, they're done. They say it is the shifter causing this. It has had something done to the shifter before I purchased the car so I don't know what has been done. Vibration is not inproved. Any thoughts as to where to look and what this could be? Again, no problems prior to the first visit for repairs.

Thanks, David