My prius does well at high speeds, but your MPG will fall below 50 at these speeds. It can handle continuous grades at 85 with the only symptom being a little engine noise (higher rpm to generate the required horsepower). Enjoy this great car.

JeffD

ps - I have done several round trips East Coast - Chicago (900 miles) with 3 adults in my prius. The Pensylvania mountains are not the rockies, but they are a reasonable test.