Transmission temperature

You can check to see if the torque converter is locking by slightly pushing on the accelerator pedal while cruising at a steady highway speed. If the rpm increases with accelerator movement then the torque converter isn't locked up, key words here are slight. As you push harder you should see a jump in rpm which means the trans either down shifted or torque converter unlocked. If at cruise speed the converter isn't locking then the slippage is causing the heat problem. The hotter the fluid temp the shorter the trans life. If in fact the torque converter is locking up then either air flow or to small of a cooler is the culprit.
Blessings; kdk