Spark Plug Failures?

I own a '00 Dodge Dakota Quad Cab. It has the 3.9L V6 with the 4 speed auto.

Dec 2002, at 64k miles I had the engine tuned up. Within 4K miles, the engine ran rough at cold startup and developed a severe miss and the Engine Failure light lit off. I took it back and the trouble code was a "Misfire detected in cylinder #2". The mechanic determined it to be a cracked insulator on cylinder #2 spark plug and replaced the spark plug under warranty. 4K miles later, the engine started running rough at cold startup, had the same miss and the engine light lit off again. The trouble code was again "misfire in cylinder #2". Pulling the spark plug, it was found to be a cracked insulator once again. It was replaced once again under warranty. The mechanic could offer no explanation for a double failure of this type.

I have to believe the odds against 2 defective spark plugs winding up in the same cylinder on the same engine failing in the same mileage are astronomical.

All routine scheduled maintenance has been performed on this truck.

Has anyone else run into circumstances as I've described or have any ideas what could be causing a failure of this type?

(if they were broken on the outside) Your mechanic didnt use the rubber insulated spark plug socket, is my guess that the insulators wre minorly cracked on installation and the heating and cooling of the motor finished the crack the rest of the way though. :headshake

Sounds like a incorrectly installed spark plug. Was it the same mechanic who installed both spark plugs?