I was just told by my gm deal ship the vibration is coming from the prop shaft ring and pinion. They can replace it the only question is how long till it starts again. I asked about tires they laughed and said that's what other dealerships tell people. They said there will be a fix in time but for now call gm and complain. The shaft is junk they can replace it 100 times and it'll still go out. They showed me a 2015 with 300 miles that's been sitting there for a month waiting for the right parts. Guess ill just call and tell them my vin and see if they ever fix it.