OK, sounds like everyone has done their homework and has guessed the same things I did.
The problem turned out to be one little part........
The Distributor Rotor.
I was not convinced it was the ignition at all, and even less convinced that the problem was in the secondary side.
I would have never thought a rotor could bring a car suddenly to its knees. Or make it (sort of) run only on Champion spark plugs. Or run fine when you kept your foot on the gas all the time and braked with your left foot. And why did it run fine on the highway but not in stop and go traffic? Seems like the load would be higher on the ignition system at high speed/high load.
I had to go to Autozone to get a replacement over the weekend (not Bosch). I had checked the old rotor. It looked good and the resistance was just over 1Kohms (within spec). I had little hope that the rotor was faulty but, in desperation really, I replaced it. The car ran perfectly! I put the old one back in and once again, it was going nuts, coughing, missing and spitting. So I installed the new one again and - smooth as silk.
So, there is a lesson here for us all. Check the simple things first and don't let anything surprise you.
I love a good challenge and it felt good to win! And this was not nearly as much work as that evaporator!
