Most of the quickest titans run the JBA cat back. This site has the best price i have seen.
http://www.performancecenter.com/pr...Nissan/2004/Titan/5.6L/King+Cab?brandname=JBA
http://www.performancecenter.com/pr...Nissan/2004/Titan/5.6L/King+Cab?brandname=JBA