Those are good numbers, even if the computer is off by a little... Perhaps every car is different, but my trip computer was consistently showing about 2 mpg higher than actual.
I couldn't figure out why my tank was running out so soon while my computer's mpg was so high, so on a couple of 1800 mile drives (SF to Tucson and back), I calculated it by the miles driven vs number of gallons to fill the tank, at each refill, and yeah, ended up my computer showed 30 mpg, but by the actual 'gallons to full' vs. miles traveled, it was actually 28. Mine is an XT.
I learned quickly that cruise control pulls down gas mileage, for me. Using the "green bar" on my trip computer to modulate speed vs throttle input for max fuel efficiency worked great. Was a fun little 'game' to play on the long drives, too.