To test the TC (torque converter) draining theory. Check your fluid level before you start the car and check it after about 20 seconds you will see a drastic drop in level if the TC is sucking it back up. Like stated before the TC can hold up to 4 quarts of fluid.
Anyone who has changed a transmission can attest. When filling it up for the first time the fluid vanishes quickly because the TC it pulling it in.
So if your situation is true. You're TC emptying problem would be like filling the transmission for the first time every start up.
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