Im pretty sure you wont be able to clear 35s with just a leveling kit. Gm trucks dont have that big of wheel openings. You should have no problem running 33s with a leveling kit. If your gonna run 35s, I’d take a look into like a 4" lift at least. Also, if you are going with 35s have you thought about changing your gearing? I know I read on one of the forums about going with bigger tires screws with the allison tranny. You should take a look into it to be on the safe side.