The torque converter transmits power to the transmission. It does this through the transmission fluid and prevents the engine from stalling while shifting between gears. When the converter isn’t working properly, the transmission overheats and shifting fails.
A torque converter repair is expensive, so it’s important to find out if the converter is actually the problem. Transmission problems are hard to diagnose, so make sure a professional ASE-certified mechanic inspects it. It may turn out to be another issue.