I have a transmission cooler installed at 8000 miles and I change my transmission oil every 20,000 miles. I do lots of slow steep hills and since I live in a tropical area, average temps are around 34. Also the hill climbs are behind slow moving vehicles so not much airflow, I also face lots of stop and go traffic and my OBD reader would show temps of 90 plus in traffic and hills and therefore got myself the cooler. Its so heartening to see the transmission last this long with the OEM radiator based transmission cooler and regular oil drain and fill so I hope my transmission would be trouble free as well. In hills I drive with the OD off.