mmmm... i'm surprised you are getting better gas mileage. as i understand it, and as it works on my 1992 trooper, the power button changes the shift points so that the transmission stays in a lower gear longer on the rpm/torque curve.

this should mean that your mileage would suffer. it is not an economy feature at all.

is it possible your mileage shows improvement because you're paying more attention to the way you drive. . .or is it because you haven't taken your new tire size into consideration when calculating your mileage-- i.e. your actual miles are different than what your odometer now shows. larger tires = actual miles greater than indicated.

btw, this affects the speedo, too. and you're actually going faster than it shows.