Dear Chris,
How different are two torques that you are comparing?
Is the drivetrain or generator DOF enabled in FAST? The rotor torque output by FAST not only includes contributions from the aerodynamic loads, but it also includes contributions from rotor inertia if the rotor is accelerating or decelerating. This is exexplained in detail in the June 10 post of the forum topic found here: FAST-Aerodyn Beddoes Stall Mode.
Best regards,