Pac996

Instructions on stabilizers and other additives mention having the fuel level down a certain amount then pour in additive and then top off with fuel to assure the added gas mixes the additive. Filler necks don't arrange themselves to mix gas. A low level of fuel assures the additive will be stirred when adding gas. Lots of injector and engine cleaner stuff is oil bases heavier than fuel and requiring to be stirred up off the bottom.

How much fuel was in your tank before fuel additive? Could of been your only problem. Just in case you pay time and money into tryin to track down the cause and it was just the additive surged out of a crease in the tank and overwelmed you engine.

fpb111

I vote phase separation or settling of the stabilizer that caused an injection of "nonflammable fuel" to foul a plug(s). Which cleared up with remixing while driving thus transmogrifying the "fuel" into something that would burn. Get the engine good and warm then run it up to 5 or 6k under load a couple of times.
Are you due for spark plugs?

Airrik

It could also be a bad ignition coil. Get a code reader.

Pac996

MAF sensor got cobwebs on it?
Caught the squirls sleeping and sucked in their pajamas?
Anything loose on the intake plastic?
If you haven't treated for water and the srts maybe the additive absorbed all the gunk into the fuel at the bottom. I've seen water look like a gel on the bottom of a tank shifting around when the tank is moved.
Like always we all always love to give you the maximum amount of things to check
Air, fuel, ignition. Do the simple checks first like air filter, maf sensor cleaned and such.

Nice to hear it cleared up.