It is typical for the MPG gauge to be optimistic on Toyota Hybrids.

Also,the vehicle typically travels farther than the odometer reports by a small perecnt (1-2%) New tires rotate fewer times than worn tires over a given distance.

The MPG gauge on my 2006 Highlander Hybrid is optimistic on average by 4% over manual calculations. This is an average over 48 tanks of gas (600 gallons).