The way you are describing it... it ran great on 93 octane? I had a similar problem. I would get nasty misfires under heavy acceleration, unless I ran 93 octane gas. I found my spark plugs I had recently replaced were a bad type to have in the engine, so I promptly replaced them with motorcraft OEM replacements. Champions are JUNK! I also later found out my coil pack was bad. I picked up a slightly used ACCELL coil for $20, Runs like a champ now... Another reason for running great on the 93 octane gas may be advanced timing. Normally if you advance your timining it a little, this requres higher octane gas... hentz is why it ran great on high octane a like junk on low. So First thing is first, I would suggest finding some Motorcraft spark plugs. or even the old ones you had in there before. Then a new Coil pack, then checking your timing, a fuel filter would be a great idea as well.
