In order, all dealers have a rep from Chevy for service related issues, they are next to impossible (in my experiences) to speak too. They get involved when you escalate the problem beyond the dealership to give final approval for repairs, buy backs and so on. I am not sure where you are at with the process, and I know that most do not like being the squeaky wheel, but these trucks are not cheap. Unfortunately, you can not take the truck elsewhere at this point for repairs without Chevy's blessing, and I am really surprised another dealership tried correcting another dealerships work when it was a warranty repair. Don't bring up this site to the service manager, they hate the site and all of us arm chair quarterbacks on here that know everything. It could be a simple fix, maybe tire pressure, but more than likely bad tires, or ones that need to be "road forced balanced" by the dealership. You are walking a very thin line if GM hears you are attempting repairs without them knowing. Good luck, be patient, if you play their game, you will get the truck that you want.