Sorry - with the converter unlocked you might be 0-300hp below what you would be with a six speed. The converter unlocked is allowing it to slip. Just depends on how tight the converter is up top but they all slip if it is not locked. Throw in the fact that its a mustang dyno so a dynojet would read higher too. My bet is the motor is making way more power than the dyno is reading at the wheels.

Again go to the track. Big power autos are not dyno queens.