You drove the car around with crappier gas, and the car felt horrible. You got used to the way it felt, but over time the ECU adjusted its LT trims and it's back to normal. To you, it felt as if the car got better, even moreso than when you put 94-95. Although adding 94-95 wouldn't be any better than 91, if your tune is for 91. The extra 3-4 octane would serve as a knock buffer.