I strongly recommend contacting the BBB once your vehicle is eligible under your states lemon law. Once you are in the "legal" dialog, verses the customer care dialog, progress is very fast. I received a 100% repurchase agreement. Document every conversation with salesman, service department, and GM; document every repair action; and know the lemon law.
As I am doing research to purchase another vehicle, I see GM is not the only manufacturer with vibration issues.
http://www.tacomahq.com/3392/toyota-tacoma-driveline-vibration-tsb-2005-2014/
http://www.tacomahq.com/3406/2012-2014-toyota-tacoma-shudder/