You're gonna have to go up quite a ways to fit 33x12.50's. I have a 5.5" lift and it still rubs on the swaybar and other places before I cut up the inside of my fenders. Course, that's a suspension lift. You could go with a 2.5" James Duff lift and a body lift, or do what Alec suggested, but that's gonna include a body lift. It's pretty much personal preference whether you want to do a body lift or not...some people will tell you it's a good thing, some will tell you bad.
There's a few other ways you could do it, like doing a 4" suspension lift and a 2" body lift or something. But anyway you look at it, you'll have to go up at least 5-6" wihout having to do major trimming. You could get away with 4, but you'd have to do a lot of trimming...maybe. I'm not giving any guarantees because some trucks are different...and I don't have any experience with anything but the 5.5", but have done a lot of reading.
Or you could get 33x10.50's and you wouldn't have to lift it as much... 12.50's are just harder to fit under there.
As I said, I have the 5.5" superlift lift, and I am having to extend my drive shaft. Some others have not had to. What else you have to do is dependant on what comes with the lift you buy. You'll have to get extended brake lines, get new shocks, drop pitman arm. You also might have to get alignment shims after you're done. And one other thing, it won't stay aligned for as long as when stock. You'll have to get it aligned fairly often, so a good lifetime alignment deal from somewhere (Firestone does it, I've heard of other places as well) would work good...
Well, hope I helped.
Hell, I just hope I made sense
