Sorry to hear that. I'm averaging about 4% less than epa. I however CAN get significantly more I just don't drive those kind of trips very often at all. I can get higher than epa hwy numbers on EVERY new toyota. Quite easily. I make it a challenge every time I borrow a car from region(Toyota's SF regional office)and drive it around.
I should clarify, after toyota care is done they'll change it every 500 miles if you're willing to pay for it.
By now, I have more or less learned how to drive the 'c' in a number of optimal regimes. I also no longer take her to the areas she doesn't like going to, i.e. mountains. The weather is near-perfect for Prius driving right now. With my driving time (not distance) split evenly among 70 mph interstate, 40-55 mph highways, uncongested city and congested New Babylon (sometimes referred to as Northern Virginia) I have been getting above 55 mpg, which soundly beats the EPA figure.
I don't think there would be any reason to change oil every 5K, if you use synthetic oil. The engine runs most of the time in the optimal rpm range, and there are no dramatic cold starts.
I have been changing mine every 5k miles since day one, too many Prii burn oil as they get past 100k miles. Cheap insurance to me.
And today, when we pulled into the car port in the end of the day, this plump little girl showed exactly 10,000 miles on the odometer. Which happened exactly in 3 months. If this trend continues, we'll be out of 36K mi warranty on Jan 1, 2016.
=78,600 miles I just passed 41,000 miles on my 2014 purchased in December 2013, at about 15% EV miles.