I would also swap the coils. I had basically the same issue and symptoms you described 2 summers ago. Although my issue started on it's own, I hadn't swapped the plugs before.
Here is the kit I used. NGK plugs and Beru coils. No issues since.
https://www.ecstuning.com/b-assembled-by-ecs-parts/ignition-service-kit/99760210700ikt2/
60k miles and 20 years of service isn't bad for factory coils.
Also when you swapped the spark plug tubes what tool did you use?
I used a transom boat plug, 1" lol. Wrapped it in electrical tape and plucked all the oil tubes out perfectly.