I've changed a handful of COPS on my modulars, and usually end up just replacing all of them. On my current car, I noticed some hairline cracks around the mounting tab on a few of the coils, and some of them just tested out of spec. Whenever it would get really humid out, the engine would misfire a bit. You can try taking the boots off of your COPS, clean everything, spray the rubber boots down with silicone spray, and reassemble with dielectric grease. If that doesn't do it, scan for a misfire and find out which cylinder is misfiring, and swap that COP with another. See if the misfire moves to another cylinder. If it does, replace that coil.