ACDelco 41-101 Professional Iridium Spark Plug, Pack of 1 : Amazon.com : Automotive that comes back to iridium plugs.

you may have a bad icm if they are all iridium plugs int he engine, pull the rest, check them out for damage and that part #, if they areall good put them back in.

did you gap the new plugs when you put them in? or just went with what they are from the box?