[obermd]

Yes, the Prius is a big fat liar on its speed and mpg. Apparently there's a flaw in Toyota internal fuel calculations on some vehicles (not just the Prius).
What were the elevations and speeds like on your route? I ask because on first glance that seems like terrible mpg for a Gen 3. Off the Interstate I'd be expecting comfortably over 50mpg. (I'm mid-high 50smpg right now).

The Prius had a kayak on the roof. Anything on the roof of a high mileage car will destroy the car's efficiency, especially on the highway. For this reason, as well as the intervening years between the two vehicles, this isn't a valid comparison.