I had the igniter/coil assy checked by an electronics person and everything is good. I've double & triple checked all fuses, connectors and looked for damaged wiring. I just can't find any problems. Pulled the distributor and took out the signal generator. The resistance range is 140-180 ohms. I'm getting 155 ohms there.

Since I had the distributor out, I disassembled it as far as I could (couldn't figure out how the gear is removed) and cleaned up all the oily soot 270K miles had left inside. When I took the vacuum advancer/signal generator mounting plate out (similar to a Timken bearing in the way that it works), there was all kinds of residue on it also. It's movement, although small when actuated by the vacuum advance, was a bit rough. I took it apart and cleaned up the races and the 45 little ball bearings inside. I could see obvious wear on the races, but upon reassembly, it works much smoother than it did. It isn't a part I felt needed any grease because of its limited travel and I think the grease would only act as a dirt magnet and cause problems with its operation later on.

Anyway, I appreciate your response Buck. I thought I'd have gotten more by now, but I guess that given the info about everything I've checked thus far, this problem has many scratching their heads.

So tomorrow, I've decided to bite the bullet and take the truck to the dealer. I'll keep you all posted as to what they find.