you could blow out the gears on your rear, you need to up the ratio from what is probably a 3.55 or 3.73 to at least 4.10's like Jason said but i'd recommend the 4.56's also
also just like Jason said it is to compensate, so without doing this your engine and tranny have to work alot harder to turn the bigger heavier meats.
the Ring and pinion/ gears set will run you roughly 100 and installation could easily double that because it is no easy task.
there is soooooo much to consider when lifting if you want to do it the right way the first time instead of replacing obsolete parts as you go. I think your lift being I beams will be cheaper than one for me would be, but I figured close to 3 G's in parts alone ( including wheels and tires) and if you are going to pay someone to install it for you you can assume it will be an extra 1-2g's
other things to consider are braking system, engine cooling, rearend, engine performance upgrades, exhaust upgrades, traction...etc.