Well I had said that I didn't notice a difference when I switched from 91 to 87 octaine. Well I decided to try a tank of 91 because it was a good price. I have been running on it 2 days now. I am not 100% sure that its not where I bought it as opposed to the octaine level. I got this 91 at a different station than I usually go to. Well for that last 2 days my truck has been driving smoother and also feels more peppy. Not anything outrageous just enough to tell a difference. Maybe I'm crazy or maybe its just a better gas quality at this station, but I believe I will start using 91 for a while. What do you guys think about this finding.