I dont know if this is related to the six litre tune up or not but I did this tune up a few months ago and lately my engine has been idling rough. Today is the second time it has thrown a p0300 code (multiple cylinder misfires) since I did the tune up and it never did this before. I read another thread that someone had misfiring codes and it was an issue with regular plugs and there problems were fixed going back to the motorcraft. I had removed the original platinum motorcraft plugs and put in cheap autolites and regapped like the 6 litre recommends. not sure what to do now. just figured I'd just wait and see what you guys have to say before I go and spend more money on plugs. oh and also I used the MSD replacement coil in the tune up which I later read some people had some problems with.