[Power Hungry]

I'd have to say that is the first time I've ever heard of that, and frankly I'm calling on that one.

Spark plugs come in a number of heat ranges, regardless of manufacturer; NGK, Champion, AC, Motorcraft, Bosch, and Denso all have temperature options. As for your truck, I'd stick with the Motorcraft plugs and just go one range colder if you have any concerns. I've never had any luck with foreign plugs in Fords (ESPECIALLY Bosch) and the only thing I ever found that ran well on Champions were Chryslers and lawnmowers. However, that choice is entirely up to you.

Now, the one thing Unlimited Performance didn't tell you is that the reason headers get damaged is from the engine running leaner after the headers are installed. It has nothing to do with the spark plugs. Lean engines run hotter... Rich engines run cooler. The heat range of the spark plug determines its ability to resist fouling from deposits, not how hot it makes the combustion process. If they're handing you that garbage, then I'd seriously look elsewhere for performance products because they don't seem to know very much about how an engine works.

Prime example... If you've ever looked at a Harley, you'll notice that the stainless exhaust pipes will turn blue just off the heads. This is caused by the exhaust heat and is pretty normal with the blue coloration extending down about an inch or two. Now, on an engine that was tuned pretty lean, the stainless exhaust pipes turn a really dark blue (almost black) and the coloration extends several inches. These same lean bikes also tend to backfire on deceleration.

I hope this helps.