Ok I just replaced my plugs, gapped at .055 and my wires and now I am running rough. Check engine light came on ( 10pcm do300 hc ) which tells me an engine misfire is detected. I have checked the wires to make sure they are fully seated and I have run out of ideas. Any help would be greatly appreciated.

 

Turns out I cracked a plug upon installation. Also I regapped all plugs to .060 and she is now purring like a kitten.

 

Ceramic is extremely brittle, so it doesn't surprise me that this was the culprit. It's good to see you figured it out. I recall many years ago having the same issue after installing a brand new set of plugs in my 68 C3. It turned out that one of the plugs was bad. There was not external clue as to why it failed but a replacement left the engine running perfectly again.