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If the torque converter clutch is staying on it can be caused by the converter itself, the solenoid that controls it or a sticking valve in the valve body. A complete overhaul isn't usually necessary unless the converter material delaminates and spreads through the trans. This can happen if the car is driven in this condition for a while without repairing it but you wouldn't know if there was debris unless at least the pan is dropped.
If it was me I would first drop the pan to see how much debris is there. If it's clean then I would go through the valve body and replace the solenoid. The converter clutch could be damaged and require converter replacement, if it shudders or slips on engagement once it's working again then it will need to be replaced.