I would say +20. The less offset the more your wheels stick out and the closer the tyres get to the mudflaps at full lock. You will probably need to trim/remove the mudflaps and trim/massage sill and maybe a bodylift, suspension lift won't stop rubbing when articulating front axle as the range of movement remains the same just stationary height changes. I would be increaqsing the engines power with exhaust/chip/intercooler and fitting crawler gears to the transfer case before fitting 33's, otherwise you will end up with a truck that is ALL SHOW AND NO GO.
Cheers