"IF" you think about gambling on a GM, there will be 3 out of 5 on the lot that vibrate.
the vibrations start around 70mph for most and they do vary so some its 80 and some its 65 or 75 but the important thing to point out is that even people who tested for vibrations and "thought" they had a good truck had the vibrations start only after several thousand miles.
beyond the vibration issues there are many other issues going on.
I would suggest you look at ford or dodge and not go anywhere near a GM truck, the 2014's and the 2015's have the same unresolved issues but at least the 2015's got rid of the HD radio so at least the radios work in the 2015's.
again only if you want to gamble on a GM, look here and see the long list of things to test before buying and problems you will likely have to fix yourself out of pocket.
http://www.gm-trucks.com/forums/foru...ice-bulletins/