33"

I just bought a 2008 Tahoe and it came with 305/30R26 rims and tires which is 33.2" overall and they need to go!!!! I want to put on 33x12.5R20 my question is do I need to put on a leveling kit or lift it to get them to fit? The 2 offset options I have for the new rims is either +18 or +25. Any...