The Horsepower peak of a TR is only 4400 RPM while the 2-3 shift isn't until 5000 RPM and there shouldn't be a 3-4 shift.
Locking the converter keeps the motor in its power band longer.
By keeping the motor closer to its HP peak, more work is performed by the motor and the run is Quicker/faster. Trap speed is also increased because the motor hasn't run out of breathe, yet (over 5400 RPM with a stock motor and a small turbo, a LC2 motor is DONE with HP and torque falling off a cliff)