For the 02-05s, guys typically can fit 33x12.5x17s on the stock suspension and 35x12.5x17s if they level the front by cranking the torsion bars or using new torsion bar keys. Some feel the 35s look too stuffed, but to each his own.
I have heard of many guys just cranking the bars and it has been fine. The only issue, which is an issue with cranking or with new keys, is that you might need longer shocks since the OEM ones tend to bottom pretty easily. I know that a couple of the higher priced key sets include shock extensions, but I have not heard of someone that just sells the extensions. Another minor issue is that sometimes one torsion bar does not lift as high as the other even when cranked all the way. The problem with that is you will not have much adjustability on that side when you get an alignment. Oh and either way, you WILL need an alignment