It takes a lot of lift to clear 33s on a Silverado. The Silverado is a big truck and the 33s are big tires. You're going to need at least a 6-inch suspension lift to clear them. And even then, you might have to do some trimming to the body or fenders to avoid rubbing. But with a little work, you can get it done and have a truck that looks great and can handle just about anything you throw at it.