Last year I swapped in a Walbro 255HP into the fuel tank, after the stock pump died. Since then, I've been getting shit mileage(20mpg @ 75mph with or without AC). I've tried all of the usual suspects (o2 sensor, temp sensor, readapting, different DI cassette, etc). I don't see why replacing the fuel pump would cause the mileage drop(if I do 55mph i get ~25mpg), so I'm not really sure what else it could be? I've checked for leaks, and there are none that I can find.