As cheap as plugs are i'd replace them. And the AC Delco's should be waranty'd if you have the receipt. Take them back and say you have a bad wire. You can also check all your coil packs for rust and take steel wool or sand paper to them. Unbolt your Coils look for rust and debris and do the same thing.

Or you could just get some junkyard ICM or coil packs. Do you know what cyl is misfiring ?