Immediately stop driving. Continuing to drive an overheating transmission can lead to catastrophic internal damage or even a vehicle fire.
Use an OBD-II scanner to check for "P" codes (e.g., a TCC code). These will tell you if the computer has detected specific gear ratio errors or sensor failures. Common Solutions
If the transmission shifts but fails to "lock up" in higher gears, it can generate immense heat very quickly, eventually leading to smoke. This is often an electrical issue involving solenoids or valves.
Look under the vehicle for puddles. If transmission fluid leaks onto hot exhaust components, it will produce significant smoke. Common leak points include: Transmission pan gasket Cooler lines Output shaft seals