I cannot determine if Quiktrip was the true reason why my gas mileage went down noticeably, but I went back to using Murphy USA (Wal-Mart) gas and my gas mileage is up to what it was before I used Quiktrip.
Here is what has made me question this. I was always using Murphy USA and was averaging 22 mpg, I then switched to Quiktrip, and every average was 20 mpg or below. I managed 21 mpg one time with an average of two fill-ups, but one of those fill-ups was at Murphy USA. This is not scientific, it could be because it was the winter blend, but I had started using Quiktrip at the end of summer, and noted the difference then as well. Also, I always filled up at the exact same pump, and my driving styles were pretty much the same. All scheduled maintenance was performed and there was no decrease or increase in gas mileage.
I use the Amsoil Performance Improver, did not see any major differences with it, but I do know that gas quality is never consistent. I haven't used the Fuel Power before, but I'd trust Terry on his stand of getting the cheapest gas he can find and using Fuel Power.