Yes, plugs pulled, cleaned and checked for proper gap.
Erbman has posted several times about a possible fault with the plug wire ends that some have had problems with, where there is a capacitor or something in the cap, that some people have removed, and replaced with a solid piece of copper wire cut to the right length. Hopefully, he or somebody else who has knowledge of this will chime in.
Have you tried switching wires as well as coils...ie leave the coils in place and swap wires to see if it makes a difference?
I purchased a Clymers shop manual, that has the various test for continuity, resistance, etc., for the different components in the ignition system. If your going to do your own work, I'd recommend it. Get the second editon with the colored wire schematics in the rear. There is a test for the coils and the wires. People have links to an online manual somewhere, but I don't.
Resistance between each end of the spark plug cap, should be 10 k ohms.
Resistance for the primary/secondary of the coils should be....pull the caps off the plugs, and disconnect the spade connectors from the coils(keep track of what goes where)....for the primary, with the positive lead on the red/black wire, and the negative probe on the orange or grey wire, the primary coil resistance should be 1.32-1.78 ohms(same for the front and back coil).
For the secondary, measure the resistance as follows. Remove both plug wires from the plugs, and check resistance between the two plug wires(ie current passing from one to the other through the coil)the secondary resistance on each coil should be, 12-18 k ohms.
If its out of wack somewhere then replace the bad one.
I noticed above where you have checked the wires. If you can lay your hands on a used ignitor(ignition control module) that works, it might help. There are other test for the ignition system, but this seems to be down stream(spark plug end of the ignitor) from the rest of the components that feed the ignitor information. I'd think if there was something else, it'd work against both coils, instead of just affecting the front one.....I'm guessing here
Check all the wire connections to make sure nothing is loose between the ignitior, and coils.
The ignitor may be at fault here, and was getting worse as time went by, creating the carbon issues in the front end. If its been firing inconsistently, that'd give you the mess your dealing with I think????????
If the electric is good, and your confident in it, then you need to step back to the last thing that happened up front, and that was the head work as a couple of guys mentioned earlier, something may be out of adjustment.