Dirty MAF sounds like the culprit to me. Did you ever get a violent "jerk" as if the car shut down for a second at WOT? Also, CAS connector is notorius <------(not spelled correctly) for heavy oxidation, which gives a similar feel like the one you described. The Connectors at the PTU are also likely culprits to make it run bad due to heavy oxidation. Nice Spark Plug!! You running rocket fuel??? haha. Hope this helps. Oh, and check your grounds.