has any change been made that would lower the gas mileage from the 2007?

dont know of any,mabey you have a larger engine,or bigger tires on the 08.

Could also be that the '08 is not broken in yet. Gas mileage typically increases over time as the engine breaks in, topping out once everything is fully broken in, anywhere from 3,000-30,000 miles. After that it stays pretty much the same unless an outside factor like a bad spark plug, dirty air filter, etc. causes it to decrease. Give it time, you may see your '08 get the same MPG as your 07. I am not aware of any design changes that would affect this.

My 2011 Prius (bought used with 74,000 miles by 2 prior owners) has been averaging no better than 39 MPG. I read the entries on some Prius chat sites and I IMMEDIATELY went to my local O'Reilly's Auto Parts store in order to buy a bottle of injectors cleaner. The attendant recommended me LUCAS after I told him that the car was a 2011 Prius. With a teacher and/or senior citizen discount, I paid a $6.74 total. I immediately poured the fluid into the 3/4 full (COSTCO regular unleaded) tank. I started a new trip with 000 miles and drove the car for five miles on "EV / ECO" and I soon noticed that the CONSUMPTION marker went up to 55.1MPG by the time I stopped at my house. At almost 8:30 PM, I wanted to keep and keep on driving! I drove the car on the city street at normal traffic speed, the AVG MPH marker indicated 37. The current temperature in the Coachella Valley is 77 degr/Farenh. I cannot wait until tomorrow in order to drive it for a longer distance and to compare the MPGs since I bought it about 4,000 miles ago. The system indicates that the best average for this car has been 49.5 MPG on a trip of 314 miles.... way before I bought it. I hope that this entry is able to help somebody out there.