Are my spark plugs still misfiring?

[72timemachine]

Update on the misfire. I am using the factory spec spark plugs, AC Delco cr43ts. These are spark plugs with a built in resistor. Turns out that when I started the engine from dead cold in the morning, the truck ran great until it came up to temperature, then it would slowly laps into skipping from then on.

I just happened to spray some water on that, now very hot #7 exhaust manifold and noticed it was not sizzling off nearly as quickly as the others. I then pulled the plug wire off the spark plug and did not notice any change in the engine's idle.

Once the engine cooled off, I removed the #7 spark plug and inspected with a very bright light which illuminated a very tiny micro crack which appeared to be highlighted by some black discoloration within this micro crack (approximately 1/16" in length) because I could not wipe it off, it seemed embedded in the crack. I ran my fingernail over it and could feel something so with that I used the sharp corner of a utility blade to try and get a better sense of what I feel is a very tiny crack. This may have been causing the misfire or perhaps the plug was somehow internally damaged, I'm still a bit unsure. I replaced this spark plug with a new one and the misfire is now gone and the engine is running smoothly.

Has anyone experienced a resistor with the spark plug causing a misfire if I did not in fact have a cracked spark plug?