Wish I would have seen this the other day. I just bought a 2014 GMC Sierra 3500HD Allison/ duramax with 33,000 miles on it. It was snowing the day I bought it and the truck drove fine so I thought. I couldn't get much over 50 as it was icy as hell and snowing on the test drive. Its going to the dealer tomorrow. It feels like there is a problem in the left front cv shaft or something and sounds like hell now! I have vibration around 60 to 70 but it makes a lot of noise at 25mph and up. I just spent the last 2 days reading this whole forum and it sounds like either pinion/gear, torque converter or driveline..... Very disappointed I bought it now that I read this forum.