Go with the main four (I,H,E,P) and add in a custom tune :rules:. Like 98Hotrod98 said, you're not really going to see all that great of a gain from any one individually. If you did all four and went with a custom tune for your DSP, you will see good improvement. The problem with "performance" mods and MPG is that most people have a hard time keeping their foot off the gas pedal. You will want to feel that extra HP and/or hear the sound of your new exhaust. The TBS is useless on your year truck but it won't really hurt anything either, I picked one up for like $40 on eBay. I wouldn't recommend spending over $100 for a brand name one. Headers work by helping with air-flow; the less restrictions you have the better the air-flow which means more HP. The better your engine can breathe, the more efficient it can run. Go with long-tubes though.