I love the new gmc sierra's I want to do the same setup just with a 4 inch lift. Mainly because i don't want to start cutting into my new truck. I think i wouldn't mind a little rubbing depending on how severe it would be. Sick ass truck though man.
Custom offset sometimes you will have to put your truck info if you select stock suspension and no cutting on your truck then it will only give you 305/50r20