My 100,000 mile 2007 3.8 started missing, and then really started missing and threw an MIL light. I had the code checked, and it said Cyl #3 was misfiring. My plugs are about 25,000 miles (Autolite), so I bought a coil pack and installed that. No change. I installed new plug wires...no change. I let the engine cool overnight, and the next morning I installed a new plug in cyl #3...and that was the fix. The old plug had a HUGE gap...Evel Knevel would have thought long and hard about jumping this gap. The center electrode seemed loose in the plug, so I think somehow it slipped in the ceramic insulator...or ?
Just a word of encouragement to those trying to track down the source of misfire codes...they can be solved!

 

Thank you for the update. Its always good when you find the fix and share it with others.