Has it gotten past that break in period the dealer says you have to drive in order for it to finally get its best mileage? (which is anywhere from 2-10,000km depending which forum or salesman you happen to read/hear.
The "break in" period is absolute BS. Whenever gas mileage poses a potential objection to closing a sale the old "break in" BS is commonly introduced.
Next time you hear this crap nail the dealer person hard and ask them specifically to identify what exactly "breaks in" and answer's like the "motor" don't suffice. If they can't, then have them bring in the service manager and watch him try and say that with a straight face.
You will never get better mileage than when the vehicle is brand new.