wideguy

#1- I had a rear spark plug cap that kept popping off. It stayed close enough to the plug to start and idle OK, but on application of power, it missed and stuttered, just like yours is doing.
#2- I had a front plug wire (HT lead) that broke. Just the wire broke, not the insulation. As the wire bounced around, it would sometimes be a closed circuit, sometimes open. When it was open, again, identical to the operation of your engine.
#3- A bad plug, with high internal resistance or open internally would also cause what you have.

If you're not having the plug cap popping problem, I recommend you invest in new plug wires and plugs.

As a first step, you could swap the plugs to the alternate cylinders, run it, and check the plugs again. (or just check exhaust pipe temp differentials again. If the problem follows the plug, that's the problem. If it doesn't, it's likely the rear HT lead.