Distributor caps can do strange things that make diagnosing an intermittemt miss a nightmare. The old "odd-fire" Buick/Olds 3.8 L V6 from the early 1980s had a chronic problem that could make a mechanic want to invent phrases that would make a sailor blush. One of the screws that held the HEI coil into the cap was right above the connector for a plug wire, and the insulation was a bit weak on some caps. A high resistance plug wire could cause the voltage from the rotor to drill a hole in the cap material and jump to the end of the screw- - - -causing a nasty miss, but only during a hard uphill pull, trailer towing, etc. Until GM increased the thickness of the plastic in that area, it was a pretty common problem, but one that was incredibly difficult to find.
Jerry
