Since day 1 had vibration and shake like a tire out of balance. Had all tires re-balanced at a tire store. none were out, but still have vibration. Seems to go away at different speeds but then comes back when hit a small bump or crack in the highway. This is my first short box and my 4th duramax since 2011. Never experienced this before. Can't find any problem. Now have 3800 miles and am almost wishing had my 2015 back. Could this be in the drive line areas front or rear? Pull 5th wheel trailer most all the time so leaving it for days or weeks at a time is all but out of the question. don't think I'm dreaming as my bride feels it also. Anyone else having this problem, or an idea about a remedy?