You're 4WD, so you can do up to a 2" level kit. Start with that. You can find them used around here for a pretty decent price. With that, you should be able to tuck 35's under your truck. If you don't think 2" kit is enough, look at the 4" spindle with a 2" rear block. Still pretty inexpensive, though everything is relative.
As for what you can fit under it stock, check out this thread. There's a tire fitment page in there somewhere.
http://www.titantalk.com/forums/titan-general-discussion/47863-best-titantalk.html
As for what you can fit under it stock, check out this thread. There's a tire fitment page in there somewhere.
http://www.titantalk.com/forums/titan-general-discussion/47863-best-titantalk.html