I was driving down a rural 2 lane road in my Monte. Just cruising. I caught up with an 18 wheeler and was looking for an opportunity to pass. When I was able to get around the truck I gave about 4/5th throttle and the Monte was pulling hard and then, all of a sudden, it lost some power and started missing. I pulled over, shut it off and popped the hood. No spark plug wires were loose and I didn't see a vacuum line loose. I started it up and headed home so I could do a more thorough inspection. I found nothing wrong externally so I pulled the plugs to see if one was fouled or loose. The number 3 spark plug apparently made some contact. I don't think anything was broken but this is scary. I got lucky I guess.