Actually, the higher stall TC and gears DO make more horsepower,by
virtue of torque multiplication they automatically increase horsepower by extension.So
there is a REAL change in horses at the wheels
An engine only makes power, gears divide that power between top end (high ratio) and acceleration (low ratio) they don't make any extra power. Take a car geared for the 8th mile and now take the car to quarter mile track it will run out of rpm a little over 1/2 way so you wound need to install higher gears given up acceleration for top end. Gears just suit the powerband of the engine to the job required. And with the torque converter is making some kind of trade off for extra torque but ain't making any extra power.