Regardless of level at 1" or 1.5", you're limited to a 33" tire. That's the same height as the 275/70R18s which came on the truck. You could go wider, to a 305/65 (12x33) or a 325/60 (13x33) but with either you might need to do a little PWM. With the 325, I'm betting you'll need to do some cutting of the pinch weld. And the 325 is too wide for the OEM rim, so you'd need a wider rim to really make those work.
To go much taller than 33", you need 4-6" of lift.
To go much taller than 33", you need 4-6" of lift.
