He posted in the intake and exhaust, not the 6.5l section, so I'm going to assume he doesnt have a 6.5l and probably a gasser. If so, we need more details on the truck, whats been done, and future plans before anybody can make a suggestion. A 99 Sub could be 1500 or 2500, 5.7l, 7.4l, or 6.5l with a turbo. Need alot more info to give any response.