So let me "set" this straight. The 3rd truck vibrates when you go over 70 MPH. I did not drive it to an interstate where I could maintain this speed during the test drive. The other 2 vibrate starting around 40 to 50 mph. I do have faith that my dealer will get the problem repaired. So far they have not let me down. We purchase a lot of vehicles from them and use the service department religiously. I have 24 GM vehicles to maintain and have found them to be more honest than any of the independents we have tried. It also doesn't hurt that I bought a truck that had sold for $44K 13 months ago and I paid $30K for it with 7,900 miles on it and was given all the factory warranty back. So for that, I can deal with them working to fix the problem that was created by a GM supplier. They also give me what ever I want to drive when it's there with the exception of a Z06, Z28,ZL1 or CTS-V. And if anyone is interested the dealer is Bradshaw Automotive