Hi,
One of the reasons I plot 'mph vs MPG' is to determine if the problem is vehicle or something else. My first fill-up in the 2003 Prius was the first car data point in this chart:
The first data point was the airplane trip out to get the car and drive back. My first fill-up was the 39 MPG mark at 75 mph.
The first thing I do is ask the complainer to drive a circular route, a by-pass, that is relatively flat at a cruise control speed. Do one warm-up pass and then reset the trip meter. Once they realize the vehicle CAN achieve the predicted mileage, they start listening and to a greater or lessor extent, following good advice.
This is the detailed chart for the NHW11 Prius:
This is my ZVW30, 2010 Prius, chart:
Bob Wilson