My gas mileage seems to be all over the place after my fuel pump got replaced.

What is your question?

I have a 6.0 liter engine and was getting 6-12 mpg in town and 14-28mpg highway. My fuel pump was just replaced and I am now reading 18-27 mpg in town and 6-7 mpg highway. Idle is high and car self propels. I can drive several miles without ever touching the gas pedal and when I made a u-turn after driving without touching the gas for at least 3/4 mile it picked up speed. I think the mechanic may have installed the wrong had pump because he seemed very surprised when I mentioned that my car had econo boost. Any advice is greatly appreciated !