aweb9, in order to fit 33's you'll need to do a torsion bar/ shackle lift along with the 3'' body lift. about regearing, it depends on what gears you have now stock. if you have 4.10 or maybe 3.75 gears, you should be ok, but otherwise you will want to upgrade to 4.27 or even 4.56 gears. im not sure how much regearing costs, but i think its kind of a lot like 500-1000 or something, but im not positive on that.
im assuming you have 4wd though. if you have 2wd you have the option to so a 3'' spindle lift too. i think they run about 500-600 bucks. and it lifts your truck suspension wise, not your body. if you have 2wd you could to the 3'' spindle, 2'' torsion/shackle, and 2'' or 3'' body lift and you could fit 35's with that. good luck!