Why is my slanty chugging? (Problem solved, for now anyway)

the plugs on my HO367 were new in 1999, over 100,000 miles ago. Car still "misses" same as it always has...... lol, due to the size of the cam no doubt..............
@cruiser take a good look at the porcelains of those plugs; I'll bet you will find a cracked insulator. It may look like a hairline pencil track.
When that happens, then at idle, the spark can leak to ground, but when you increase the load and/or rpm, two things happen;
1) the spark energy is increased, and
2) the time to leak is reduced.
So it is entirely possible for this to fit your symptoms.
As the crack gets larger, and fills with soot, the symptoms get worse, and eventually, if left too long, that porcelain my rupture and cast off very hard glass bits..
The crack is usually caused by detonation, so if this is happening on an on-going basis, you better review your ignition timing program, or your lugging habits.
But good news, it may not be a crack at all, but just a carbon-track. You'll have to figure out which it is.