[The Burning Rom]

Platinum plugs aren't good for these motors. They don't last very long. Since the DIS system that GM uses fires BOTH plugs on a coil at the same time, even if only one of them needs to fire. That's why I like to call it waste-a-spark ignition. It could be that the platinum has already burnt out in that plug.

Or it could be that it was just a random miss-fire. Is the Check Engine Light still on? If you have the code cleared..does it come back?