Hello, I have a 07 Tahoe LTZ that we purchased in November. We are experiencing a problem the Dealer claims "cannot be replicated." When stationary, the car will shift. Honestly, it feels like the person behind us has rear ended us. The first time it happened, I actually got out because I thought I had been hit. Happens mostly 10 - 30 seconds after stopped, but has started happening upon acceleration now too. Any ideas would be appreciated. I plan to take it in again next week and would like to throw out some suggestions. Thanks!