Got home Saturday from a camping trip towing my 10k toy hauler 130 miles over a hilly route. Jumped in the truck to go to work on Monday and as soon as I start the engine it is idling rough. Bad miss all the way to work and back. The whole time I am thinking "what now?" I replaced all 10 coils almost exactly 1 year ago and about 10k miles so I was reasonably confident they were not the issue. I started to get paranoid that a plug was getting ready to eject even though I heard no noise to indicate that was an issue. I planned to re torque as soon as I got home (I had done so about 20k ago) but I started thinking I should go ahead and swap plugs and boots if I was going to all that trouble. Plugs and boots had right at 30k on them. I started replacing plugs, taking care to note if any were loose, if the boots looked weird, if the coils had any issues that were visible, etc. The plugs looked good, all 10 were identical in appearance. However, they all had a slight deformation on one side of the insulator right where it meets the center electrode. All of the deformations across all 10 plugs was identical. When I got to the 10th plug and no obvious issues I was worried. I was pleasantly surprised when I started it up and it idled smooth as glass! Took it for a test drive and it hasn't run that well for a while! Plugs and boots were factory Motorcraft and I replaced with same.
Just wanted to share in case someone was having a similar issue. Ended up being a relatively cheap and easy fix. $150 and two hours labor and I am back in business! Not sure how/why the plugs went from fine to bad and in only 30k but I am glad it is fixed!

 

What kind of plugs did you get?

 

I replaced them with factory Motorcraft. Same that were installed when I had the issue.