My truck seems to have the typical vibration. 73 plus mph, and it started at about 8000 miles. It manifests mostly in the center console. I have the folding console with the 60/40 bench. Do the owners with captains chairs have the same vibration in thier console?
Look for green or red marks on your leaf springs. The manufacturer marks them red for tall and green for short (I may have that backwards). No tag is neutral. GM is supposed to match them up during assembly. I have been to both the spring manufacturer and the Fort Wayne assy plant and seen this in practice.