Many have reported ignition coil problems and misfires resulting in all the coils being replaced at about $33 USD each plus big $$ labor. Early coils were a problem and the fix apparently occurred around 2007. So it makes sense to replace them all on a 2004-2006 if it has not already been done under warranty.

I had a misfire in #2 on a 2008 GT and replaced only that #2 coil which had a manufacturing date of 2007. But others now have 12 used coils without knowing which are good and which are bad.

Today I read how to test the coils so you'll know which to keep. Of course a good one might yet go bad in the future.

Test the resistance between pin #1 and pin #15 in the electrical connection socket on top of the coil. @20 degrees C the resistance should be between 0.3 and 0.7 ohms.

Hope that helps somebody.