Refering to the comment about body lifts and C 'o G. Consider a 2" body lift and a 2" spring & shackle lift...
The body lift only lifts the body, and allows for the desired 33s in question. The center of gravity is a little higher.
The spring & shackle lift not only raises the body 2", but it also raises the entire chassis, resulting in a final center of gravity that is much higher than just the body lift alone.
I'm not necessarily advocating the use of a body lift, but I'm saying they have a purpose. If the goal is just to fit the tires, the BL will do just that, and keep a relatively low center of gravity, for less money and work. The spring lift has some other pros/cons that should be considered. The cg will be higher than the body lift, but belly clearance is increased (better breakover angle), and depending on the springs/shackles used, flex can be increased.
I'd say if you want it to feel like the same truck, and it's a DD, do the body lift. If the truck sees more trail, or you're willing to put up with the road manners associated with more flex and a higher center of gravity, go springs, heck do both and go 35s!
my .02
