I second (or third or fourth) the motion to replace the plug wires, they should not be shocking you. Get some fire wires from sunroof GTX.

I would also replace the plugs instead of just cleaning them. I would use good plugs like NGK, don't waste money on platinums and set the gap to .040-.045 the hotter ignition will fire accross a bigger gap and the bigger gap it has to jump the hotter the spark will be and the better it will light the fire and the better it will keep the plug clean.

What is happening is the plug can fire under light load like idle but as soon as it gets more load it fouls out a plug or 2 randomly and it cleans up the next time it gets reved and another one does it. The plug wires are the spot of least resistance when the load gets high so you need to fix that leak. Think of it like a cracked PVC pipe with a spigot on the end, when there is no resistance on the end from the spigot water flows fine, when you start increasing resistance then the crack in the pipe(plug wire) opens up and the water leaks out.