08 GT. 180,000 miles. Second set since new. Motorcraft 514's. First go round at 90,000 other than 3 plugs breaking off, no other hitches. This time, again 3 plugs, but started with a very rough idle and through a #6 misfire code. Removed the plug, cleaned it, and swapped the #6 and #5 coils. Started fine after that and idles normal now. What was that? Computer learning curve?

 

Did you do a night check? See any arching? Are the wires new? Maybe not seated correctly... And the second go round you nailed it?