I went to test drive a 2014 Silverado today because I was irritated they weren't going to offer the Topaz Blue in the 2015s. Sure enough it vibrated right when you hit about 65 MPH. It wasn't super noticable. I took a water bottle to compare to some of the youtube videos I've seen. It was exactly the same. Honestly it was a bit more mild than I was expecting but I definitely noticed it because I was looking for it. Wasn't loud or anything. Honestly if I'd never read this forum I wouldn't have noticed.
I had brough this up to the sales person before the test drive and he said he hadn't heard of the issue. Actually he wanted me to take to prove it didn't do that and sure enough when I hit about 65 there it was. I said do you feel that. He said barely and that he thought it was normal.
Obviously this is a sample size of one, but have a feeling that almost all of them have it. Some people just don't notice or care and it's probably a lot more extreme on certain trucks than others. But I bet there are ton more people out there that just think it's normal.
I really hope they get this fixed. I'm really sitting on the fence of purchasing because of it. Probably going to test drive a few more and see how common it is among the trucks around here.