I'm not sure if this works with the dimensions on the '03 Denali or not, but for my truck the max is 33". A 285/70/17 is 32.71" dia. and a width of 11.22". Your stock 265/70/17 is 31.6" dia. and 10.3" wide.
Hi MAs, I know you recently did your leveling kit, but do you happen to know the max tire size you can put in with the level kit? I'm putting one into my 03 Sierra Denali, I want to keep the factory 17'' rims for now, but am wondering if I can go larger on the tires than 265/70/17 without rubbing?