Seat and steering wheel. I could duplicate any number of U-Tube videos showing a water bottle shaking in the console. It occurs at about 50 mph and again at about 75 mph.
I noticed it slightly on the test drive but attributed it to flat spots on the tires from sitting. I knew nothing about the vibration issue and called with 150 miles on the odometer. At 1,000 miles it remains exactly the same. Their response that they needed 3-5 days to diagnose prompted me to start searching for why.
Well, damn. Tomorrow I drop my three week old 2016 Sierra 1500 SLE Crew Cab with 950 miles off for 3-5 days of evaluation for the shakes. I expected a service appointment with tire balancing or maybe even replacement. Sounds like they are going full-monty right off the bat.
I couldn't resist the year-end deals and bought a Sierra 1500 SLE. I've already added a spray-in bed liner, bed cover, step rails and Weathertech mats.