For posterity, my misfire problems returned and got immeasurably worse when I did a sea foam treatment. I got misfires on all cylinders and random misfires.

This happened to me once before... Always right after a sea foam treatment. A little deduction... It was the vacuum fitting in the the throttle body where the sea foam is sucked in. It wasn't fitting tightly. I put some silicon in it and all misfires disappeared.