The truck is a 2011, I ordered the truck brand new, and had the problem since it was new. The Dealership has bent over backwards trying to fix it, but nothing is helping, they have changed tires, wheels , checked the drive shaft and just recently took a bunch of vibration readings and sent them to GM, their Engineers came back and said according to the frequencies they received it was a tire problem is what I was last told again just like before, well here is my question???, my truck has the 20" aluminum factory wheels and there is only one tire size made for that wheel specified by the factory made by Good Year, and if they keep saying it's the tires then why did they put the same wheels and tires on the 2012, 2013, 2014, and going to put them on the 2015, can one of you so called engineers explain that ????, No you can't your trouble shooting skills suck. I am a master Automotive technician an A&P Mechanic, and a Calibration Technician.It is not a vibration either it is a shake. Hint 1: Try behind the drive shaft somewhere and see what you find.