Before you do drain the gas tank can I recommend that you
DOUBLE check the charging system? Why am I concerned about the bad gas diagnosis? Because bad gas would be there all the time. The motor quitting and then easily restarting is a prime symptom of an electrical problem (battery, battery cable, or alternator problem).
While you stated that you believe the battery and alternator is good has the battery cables and terminals been checked? Almost all auto parts stores will test for free.
Other "possible" sources of this problem could be:
- Bad ignition switch
- bad CCRM
- bad fuel pump
- loose connection.
- bad MAF
- bad IAC
If this were my car before I went to the trouble of draining the tank I would at least disconnect the fuel filter and drain some gas into a clean clear container and visually inspect the fuel. Is it cloudy? Does water settle to the bottom? Does it "smell" different?
And yes it is possible to drain the fuel tank using the car's own fuel pump. Several ways to force the fuel pump to run. The easiest is with a two way ODB2 scanner. The next easiest way is to power the fuel pump directly at the round connector near the center of rear bumper (RD/BK & BN/PK)
Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/