First thing I'd do is try to level the truck using your stock keys. On your truck the "leveling kit" is only reindexed torsion keys, so all it does is allow you to crank the torsion bars further. Any lift beyond that involves differential drop, torsion key box drop, and or new spindles. Other than that you can go as high as you want, depending on the size tires you want to run and how much you want to spend.