Thanks to everyone for the great responses!

Duke: I didn't think of checking the resistance on the cap, so I will try to do that this weekend. I've also swapped a wire from a different cylinder from my old set to see if I have a bad wire.

qdessa: Thanks for the info, the original plug that I pulled had so much crud on it that it almost covered the whole tip of the plug! The originals were h9dc, so I was hoping that running h9dc0's would foul a little less.

MrCjames: You're right, there is mis-firing when the plug gets fouled up. My mechanic did a compression check and said that everything looks normal, so I'll ask about doing a leak down test if the wire swapping and cap checking doesn't work out.

myarmar: Sorry, I should have made myself more clear - I tested the wires with the resistors and connectors in place (I didn't check the wires themselves).

Have a good weekend!