Miles to empty on cluster decreases rapidly

That difference is insignificant and common. It can be a result of the sending unit sitting in a tank that is narrower near the bottom, so the fuel level drops faster. Ford also has a history of making their fuel gauges read lower than the actual level you have left. In Ford vans, for example, at "empty" there is close to seven gallons left. They do that to convince you to fill up before the level drops too low. Some gas is needed to cool the fuel pump, and if you let the level get too low, it can reduce the life of the pump. In my van, the gauge stays near "full" for the first one hundred and twenty miles, then drops rapidly to "empty" over the next one hundred and fifty miles. Other similar vans do the same thing, so it is in the design, not a defect.

As a testament to what Caradiodoc said, I noticed this when I had to replace the fuel pump in my Chevrolet Blazer. I had completely emptied the gas tank before putting the pump in and putting the tank back into place. I put roughly four gallons of gas in before the needle started to move.