Welcome to the forum! You shouldn't have a problem with 33's as long as you do not go too wide. Going any wider than a 305 will almost always require some form of wheel spacer or aftermarket wheels with a different off-set. If you have factory 20" wheels the stock tires measure around 33".
--Superchips 3865 with Advanced Transmission Tuning--K&N Drop-In Filter--Cat-back Exhaust--Sonnax Line Booster--Bilstein 5100 Leveling Shocks--Firestone RideRite Air Springs--AirLift Load Controller II--305/55/20 Nitto Trail Grapplers--
Like it was said a 33x12.5 is a pretty wide tire to use on a stock wheel. A better idea would be to look into something like a 285 metric tire. A 285 is about an inch narrower then the 12.5 and half inch on the 305.