Things that everyone has to remember is that gas is brought to major cities by pipelines, each gas company does not have their own line so odds are the gas is the same but the things they add to the gas is what differs. That is where you are going to see the performance changes. Also, places like CostCo and Sams club, they buy the cheapest gas they can find, so one week it might be good and the next it might suck. It is a gamble that is not worth taking. I use QT gas, that seems to get the best performance out of my truck, but I just got the HEMI so I need to look around, I went and filled up my truck and it costs $50 here in Phoenix.