jk2jksr

Does anyone have thoughts on this. I would greatly appreciate reply(s) to this matter: My 14 Chevy Suburban purchased 3 weeks ago CPO at 28k miles w/still warranty + additionally purchased warranty. On or about 39 MPH to 50 MPH in acceleration and deceleration, there is tremendous vibration. This happens while in local streets to highway. Initially w/stock rims and tires - same issues. And, new 22 inch rim & high end Bridgestone tires - same issues. Took it to the dealer. Inital take in, mechanics have said there is no issues and this is normal. I took it back and requested have service manger test drive with me. He agreed that I have a vibration problem. Replaced Propeller shaft. Ironic that the service dept. have said all is fixed. 5 minutes after I drove off, the same issue occurred. They are having to contact GM engineer to fly in from Detroit to review it. Anyhone with any thoughts on this. The noise is so bad, I am speeding to hit the higher speed 50 MPH + and to slower my vehicle at 38 MPH below, thus creating a dangerous driving habit.