I'll make it as short as possible. I had a similar issue with my 360 all last summer. After replacing the entire ignition piece by piece plugs, wires, dist., coil moduel, timing. No improvement. I put a scope on it it was skipping but on different cyl.all the time I put the last part on so I could tell my self it could not be ignition issue. Replaced ballist resistor and it's gone. It's a 4 prong resister. 10 bucks. Not saying it's you problem but it's 10 bucks. My experience with ballist registers was they work or not, no intermittent issues. Fyi.