You no longer have a "gas pedal". The right pedal is now a "drive by wire" pedal, operating the throttle body (for more air) which in turn is used to tell the cars ECU/PCM (brain box) to increase the fuel mixture/decrease the fuel mixture to the fuel injectors.
Before I would tear into a fuel pump, I'd be questioning the fuel filter (when was the last time it was changed), or perhaps other basic maintenance such as the air filter, spark plugs, etc.
How many miles are on this Mustangs engine? What maintenance or repairs have been done to it?
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.