Slant Six Fuel Mileage?

Those new replacement sending units are off.....they read full when tank is full but go down faster than originals and read empty when there is still 5 gallon of gas in the car......As mentioned, best thing to do is math calculation to figure out MPG.....They also make a device that will correct the gauge measurements so they are accurate regardless what sending unit you have....see if I can find it...here is a good read

Solution to Fuel Gauge/Sender Problems