Well, I dropped mine off at the dealer yesterday, and presented them with a print out of this: http://autoguide.com.vsassets.com/blog/wp-content/uploads/2016/03/PI1354C-GM-Truck-Vibration-Information-Bulletin-1.pdf
I told them that is exactly what the truck was doing. They called back before closing yesterday and said it would be awhile before I get it back because there were so many things in that bulletin that they had to do. So, they are going to go through it without even driving the truck first. Hopefully, when they are done, something in there will fix it.