To keep the subject where it started I merged the thread.

You are off a little in your numbers. I hope you don't put in 22.5 gals everytime you fill up as that is the capadity of the tank.. With that aside, the posted mpg that the manufacturer states is that of a perfect world.. THe are fule differences and winter in most states does mean different additives like ethanol.. Ethanol is used to reduce emissions but it will decrease performance and mileage.
You do sound as if there is something wrong but a little more info could help.
What brand of fuel do you buy?
What octane are you using?
What's your air filter look like?
What are you driving habits? (Jack rabbit starts, sudden stops)

The power button only changes the points at where the tranny shifts. With it on it lets the engine rev a little more to get higher in the torque curve. I've not noticed a difference as to mileage with or without....

Stay away from the snake oil products as very few of them work.