325's on 2009 Z71?

I just picked up a 09 Z71 that has 325/60/18 wild peak a/t tires on it. Everywhere I'm reading says it's a stretch to get even 305's on there. It BARELY rubs fully turned, other than that the fit is perfect. If there is a lift kit, or leveling kit, it's not a huge one as the truck does not seem that high really. Is it just the brand that fits well? I have not crawled under the truck yet, but what is done to it make these fit well? I plan on getting new tires fairly soon so that is what started my search into this. I love the look of the wide tires, and want to keep that look, but use a different brand.

PICS !!!