I have he exact same problem as identified in Silver Spaceship's original post. 2014 Silverado, purchased in November, (Special Ordered it), 5.3, Ltz Crew Cab with 308 rear end. Noticed the vibration issue when I picked it up. Starts around 45 mph. Took it to the dealer and they balanced the tires. Did not fix the issue. Took it back and they did a road force balance, did not fix the problem. They said I had a bad tire, Goodyear. I worked out a deal to have them install Michelin LTX M/S 275/55/ R20, I paid the difference, between the Goodyears approx. $500.00. Did not fix the problem, returned to the dealer and they did a road force balance. Did not fix the issue. I'm taking it back again this morning.....