Fuelly needs updated US-EPA fuel economy numbers. The ones provided are the old numbers - the EPA (@ fueleconomy.gov) has revised fuel economy estimates for most vehicles going back to 1985.
This is a frequent request. And we'll update the numbers once the EPA makes them available via their data download. Unfortunately they only make the old numbers available there, and updating hundreds of thousands of records by hand is not possible for us.
There's a bit more information about this issue in this thread and we still haven't come up with a way to update the estimates via a calculation.