Are you getting a CEL? I had the same "misfire" issue after I "cleaned" my engine bay. At first I thought I'd just replace all the COPs but after reading that you should only use the Motorcraft replacements I decided to just change all the plugs, boots and find the COPs that were acting up after that (Since I had just bought the truck I was going to replace the plugs and boots anyways). After replacing the plugs and boots I since had a misfire going on so I hooked up a scanner and it told me it was Cyl 5. I replaced the COP on Cyl 5 and it runs like a top after that. So, two things, from what I've read on here, I would stay away from the Generic Ebay COPs (unless they are in fact true Motorcraft COPs and if so at $26 bucks a pop that's a killer deal!) and get one or two from RockAuto ($42 each and cheapest I found around for Motorcraft as recommended by Forum member). Second, try and find the one or two that you might be having an issue with. Of course if you have the cash replace them all (couldn't hurt) but if you want to save a little just replace the bad COPs as they fail.