Jerry Attwater

Hello Folks, First time user here and soon to be first time owner of a GMC Sierra 1500 Elevation. Two questions I'm hoping people might have advice on: 1. I plan to level the truck and there are two options: An aftermarket kit for $800 that voids some of the warranty; or the factory levelling kit used for the AT4 (I believe) that is $2,600. Any advice on which is the most practical option? Any experience levelling 2020-21 Elevations? 2. With a 2" level, what do you think is the maximum tire size for an 18" rim? I was thinking 265/70R18 (for an Open Country) but wondering if people know of good tires with a bit more height that will fit in the wheel wells? Thanks,