I have read many of your comments, and I've decided to join the conversation.
I hesistantly traded my (new body style) perfectly operating 07 Silverado for this ALL NEW 14 Silverado in May. I noticed to vibration immediately during the test drive but the salesman assured me that it was a result of flat spots caused by sitting on the lot.
As a result of reading this forum, I decided to take it in 2 weeks ago to have this rhythmic vibration crap diagnosed. It has now been at the dealer for 2 weeks and 2 days.
I have been told that they recently received a machine that pinpoints the origin of the vibrations. This machine led them to inspect the rear end. The guy told me that one of the gears in the rear end was "ground backwards" from production. How does that happen?
Anyways, they are now replacing this gear. I'm very curious to see if this solves the problem. I have been a Proud Chevy man , like my daddy, since I was a kid. It's in my blood. However, this issue has put I very very bad taste in my mouth.
I was annoyed after I got my "American" made truck home and noticed it was manufactured in Mexico. Now, it rattles my teeth out. The cherry on top is the fact that Chevy released 2015's with the same issue. I am EXTREMELY disappointed in Chevrolet, and I really do hope my truck is fixed when I get it back.