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Actually the cap and rotor are a common cause. Have you removed and inspected them yet? Remove the coil wire from the coil and check for corrosion at both sides. If you have a spark tester you may want to use it to check for spark at both the coil wire and at one or more of the spark plug wires. A spark tester is available at any auto parts store and they are not expensive.
I would check the coil wire first for corrosion. Sometimes they arc to the trans dipstick tube and cause a misfire. Check for evidence of arcing near the dipstick tube if the wire is routed where it touches it.
Because moisture even if it is just high humidity will help the high voltage to arc to where it isn't supposed to arc to. The good news is that definately makes it sound like a secondary ignition issue. I would definately check that coil wire and dist cap. I have had many S trucks and drive a 2001 with a 4.3 as my daily driver. There are not major issues with the 4.3 distributors other than occasionally corrosion and wear to the cap which usually doesnt show up until relatively high mileage. Back in the day distributor caps were replaced every 12,000 miles. :)