From what you describe, i agree, the coil and condenser are the most likely suspects. You dont mention a coil ballast resistor. I assume your coil has the internal resistor.

Also, I would confirm that the problem exists once the engine stumbles and dies by pulling the distributor cap, manually opening the points while the primary high tension lead from the coil is gapped about 1/8" or so from the block. You can confirm weather you see a small arc on the points as well as whether you have an arc from the primary high tension lead and the block.

You can pick up a beru blue coil on ebay for 30 bucks and wire it with test wires directly from the batter to rule out any bad connections, etc.

good luck
dean