I have a 1999 Silverado C150 extended cab with a 285hp 5.3 which I have been very happt with and it has never gotten less than 14mph normally and is usually in the 15-16 range. Maybe in a very cold winter a touch less. I pulled a 1991 Corvette ZR1 back from Florida an a HD caravan trailer going up to 80mph and never got less than 14mph on any part of the trip. Got 16MPG pulling the bare trailure down to get it.
I have also got up to 21MPG on long freeway drives.
I don't know what it would do with a 250 though.
