Good call on that; I've heard of that happening too. Thanks for the reply. I did try that, replacing the wire in question with both a new AC Delco and then ZZP. Same with the plug; I used a 41-104, then an Autolite XP606. I love the XP606s and will stick with them - but neither swap cured the occasional misfire.
OH! I knew I forgot something. I compression tested all 6 cylinders (dry) and got ~160 psi for all 6. All within 5 psi of each other. Not bad for 152,000 miles on this engine! Must be the yearly SeaFoam treatment....
Thanks again. Any other ideas anyone?