You are doing everything right
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What I would do is lay off the hypermiling for a while untill you go through a full tank of gas. This way you can see what kind of mileage that the car is normally getting.
You already know this but.......
Set the odometer at '00000' when you full up, then take note of the mileage on the odometer when you fill up. Divide the miles traveled by the gallons purchased. A reciept is a good way to keep track of things like this.
125 miles is not really an accurate distance to test with, so try at least 300 .... but don't run that thing empty though !