So a bit of an update, and question. I am working on my friends 2005 Ford F-150 with about 180k miles on it, that is experiencing misfires.

I made another post asking if Bluedriver could identify a misfire within each cylinder. What I can tell is, the truck is normally not registering the misfire, it only did it when I really pushed it, but it still wouldn't throw a code so I could see where it was coming from.

I suspected bad coil packs, because it normally does it at low rmps in both 3rd and 4th gear, when applying some gas, especially on a hill.

I started checking the coil packs, and replacing the spring, and boot with Denso equipment, and I cleaned up the coil packs. I found a bad coil pack on cylinder 6. Interestingly, it had a rounded off head on the coil pack bolt, was not fun getting it off. I told my friend that I was suspicious about it, because I didn't do it. He had his spark plugs changed at about 100k. Why do I have the strangest feeling the guy that changed the spark plugs perhaps rounded the head, and never changed the spark plug? Not even sure if one could last 180k though. The coil pack also seemed...dirtier when I pulled it out.
When I replaced the bad coil pack on cylinder 6, and did a test drive, I could tell within a few miles that the issue was much better. It still misfires a little if I get the speed and RPMs just right on a hill, and gas it a bit, but it is likely 95% better. Now to deal with that last 5%.

Is it possible the last guy never changed the spark plug at 100k, and it has the original? I would think it would be misfiring like crazy.

Thanks!