I've been driving my 2008 Prius for two years and I get 45-48mpg consistently. It drops to the low 40s during winter, but besides that I've had no major hiccups. I had an oil change and tire rotation 3 weeks ago. I drove from Sacramento to Phoenix with no drop in fuel economy. A couple weeks ago upon arrival here in Arizona I filled up the tank and as soon as we left the gas station my mileage dropped to the mid-30s. I'm near the end of that tank and I'm holding at 37mpg with a mixture of city and highway driving. Any ideas what might have caused the drop? With the high heat I assume it's not the tire pressure, and I haven't noticed any changes to the car. If this next tank of gas does the same thing I was going to take it into a Toyota dealership, but I wanted to run it past you all first.