This is why in my earlier post I recommended checking for water seperation. If there was water, I would guess it came from a loose sender in the tank, loose gas cap or some other means letting water in as opposed to the gas station. If there was no water separation, I would think you got a bad load of gas and need to boost the octane. If you had water in your tank the engine would probably not run at all. If you had a bad load, it would run poorly. I've had this happen to me. Fill up at a station one time, boat and blazer. Blazer ran fine. Boat choked and ran like crap. Octane booster and a fill up of preimum at half tank fixed it.
Also had a loose sender last year, and when I washed down my deck, water went in the tank. Boat would not run and had to drain tank.
Good luck,
BT