Fluctuating neg. to ground on ignition coil

That is higher than I usually allow. I find them more commonly to be in the 5000 ohm range, + or -, for the main wires, when new.

I see this link that discusses spark plug wire resistance in some detail. It indicates that your resistance range is OK, but I never run with them with that high resistance. Usually when they get that high in resistance, they are getting a bit old. SPARK PLUG WIRES

The whole purpose of the resistance is to slow the rate of the current rise the spark, to suppress radio and electronics interference. But too much resistance, then the spark energy gets suppressed so much that it may or may not fire the mixture. This is somewhat suspicious with your idling miss....especially as it occurs with heat.

What spark plug model are you using? And to what distance is the gap set?