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So, my initial thought is distributor putting out uneven/weak spark at high rpm and moderate to heavy loading. This would also explain why the truck just felt like it couldn't handle the hills as well as it used to, even when it didn't actively misfire, plus my ever-worsening fuel "economy" (I use that term very loosely, lol.)
About 2 years ago, cutting across Wyoming in the dead of summer, I developed a slight irregular miss at highway speeds. It only popped once or twice, but I had to drop my speed to about 55 mph to keep it from happening. Got to the job, checked into the hotel, and promptly changed cap, rotor, wires, and plugs. It seemed to have fixed it, but I wasn't pulling the trailer for around-town driving, so I knew it wasn't simulating the load conditions exactly.
My only concern is what if its not the distributor itself, but the cam bearings? I honestly wouldn't have even considered the cam, except for knowing that my uncle had a soft factory cam when he got this truck from Detroit, which started presenting problems under load and led to his rebuild of this motor at 80k. How can I test if it's the distributor itself causing my misfire, or if the weak distributor is only a symptom of a cam with worn bearings warping under high rpm and load? Or maybe it's not distributor at all, but valve float ... which would again point to a worn cam?
...Any thoughts would be *greatly* appreciated.