I'm a newbie - to the site and the Prius. I bought a 2009 Prius two weeks ago. According to the MPG display I'm getting <23 MPG. I only drive ~6-7 miles/day, and have only filled the tank once. I live in a hilly city that's been in the 20's - 30's F. The Toyota dealer told me that the MPG display is unreliable and that I should go by miles between fill-ups and how much gas I need to fill the tank. Help?