Normally when you install headers you are going to have to richen the fuel trims(PCM,injectors)/install larger jets(carb) to offset the free flowing exhaust. The PCM can offset itself a bit but it runs out of compensation eventually if you have installed headers and a cold air induction. If you have done both of those without getting your PCM recalibrated you are just asking for SES codes. Break out the pocket book and get a tune from Allen to enhance your truck and really make your mods work even better for you.