Mike - I would remove the ballast or jumper around it for a test and see how it goes. A lot of high performance ignitions do not work well with them at all. I think you are on the right track in checking through the ignition.
Make sure, too, that you have a good solid ground from the chassis to the engine block.
I've seen cars that started and idled fine - run well under light loading, but when they were warmed up and driving down the street, they ran poorly. Cause in some cases was a bad ground from the block to the frame.
It's odd because you would think that the engine would not crank over to even start if there was not a ground strap. Not so - the bloody thing will ground itsef through the transmission, gears, needle bearings in the u-joints, driveshaft differential gears through the differential to the springs to the chassis!
I've also seen them ground themselves through the throttle linkage and cable - one car almost caught fire when the throttle cable lit-up like a toaster element!
