i have a 2008 gmc sierra crew cab z71 i am wanting too lift it with a 6 inch superlift and run 20x9 ballistic hostel wheels i want too go with bf goodrich mud terrain km2 tires i want too go with the biggest size i can fit can anybody tell me excatly what that is and if 325/60/20 or 325/55/20 will fit. a guy at buyitlifted.com said the 325/55/20s would but im not sure that they even make that size.