Don't get discouraged. After you find the problem, it will probably seem so small and minor... Most problems seem a lot bigger than they really are until you finally find them...
I might have missed part of your story, but are you sure you have fire on all plugs?? Do you have a mag on it? Or a distributor? Were you checking fire on the coil wire? Or each plug wire??
A cracked cap or moisture in the cap or too much carbon dust buildup can cause it to jump around randomly.
How long did it run smoothly?? Enough to tell it was hitting on all 6??