The difference is only 10% and it could be easily explained by cold temps this winter. I suspect high speed driving is the issue here. Too bad the OP never bothered to do the MPG checklist.
Google the gas stations you use and see quality of gas. I've noticed cheap gas is just that cheap but paying a little more helps the motor and helps MPG!
LNG724 - I feel your pain. We traded in a 2010 Prius III with 60k miles for a brand new 2013 Prius III and are suffering the same issues. The worst tank our previous Prius III ever got was 44mpg. It averaged 46-48mpg. This one has hit 46mpg once but typically does a lot worse. We're up to 3,000 miles now and gas mileage continues to get worse, not better. We are in winter now so I expect bad gas mileage numbers, but when we bought the car we were still in summer and the gas mileage has never been there. The car is averaging 37-38mpg now but it's terribly cold here. Average MPG has been in the 40-42mpg range the entire time we've owned the car. Toyota doesn't see anything wrong with the car. The car is driven the same exact way on the same exact paths by the same exact driver. The differences between the cars were age, mileage, and tires. The previous Prius used some Hankook tires (I cannot remember the name) that I'm not even sure were LRR tires. This one uses the factory supplied Goodyears LLR tires. We bought the car because it had the perfect options and interior/exterior color for my wife so it's whatever. I just wish the damn thing got better gas mileage. I see no reason for the drop.
I found it takes upto about 10k or even 15k miles before the car gets the best fuel economy. If you've checked all the common things like tyre pressures and correct oils and Toyota say the car is fine, then let it run in a little.
