Need help with trouble code

The mechanic did a evap system leak test with smoke detector, no sign of leak, then contacted Ford technical service hotline. Verified proper FTP voltage at 2.6 v, inspected canister purge vent, OK, inspected build date of fuel pump installed in vehicle. Pump # was old part# , so they R&R pump and reflashed the PCM to the latest calibration level. This didnt make Brenspeed very happy, had to redo my tunes. But the problem has gone from a P0456 to a P0455 code, do you think mthe gas cap my be at fault?

I finally figured out the problem. Went to the gas station, started filling the fuel tank, about 3 gallons went in then I heard a splashing sound. Another 3 gallons ended up pouring out on the concrete, looked under the car and observed a waterfall of gasoline. Called the dealership, they dispatched a flatbed tow truck, menwhile I had to get a ride home and grab the x3, and stock intake assembly. Returned to the station reflashed the PCM and installed the stock intake. The car got hauled to the dealership where they discovered the fuel pump mounted loosely to the fuel tank, thank you very much.