got my truck on Wednesday last week. Driving around town, no vibration issues but whenever going between 60-70 mph on the highway, feels like a speed strip. No sounds or anything but vibrates like a speed strip. Dealer has the truck as of yesterday and they are supposed to be putting new tires on. They think there's a hard spot on the tires. (they already re-balanced and road force balance). Not necessarily the classic shake of the silverado but just posting this in case anyone else has this issue