anyone have vibration issues with their 2014 silverado 1500?

[ski]

The reason I asked is that my brother bought a crew cab a year ago or so and is some kinda po'ed about the vibration. They have switched tires, balanced em, different driveshaft, and some rear end gear parts. He bought uniroyals for it out of his pocket. Say's it's better, but still vibrating. He's been on some forum and they figured out that the ones at the time had the tow package and there are different parts in rear end assemblies. He even bought some kinda gel pad and had a shop install it in the drivers seat.