A friend of mine owned a transmission shop so I paid him to install an extra external trans cooler, a trans temperature gauge and a deep aluminum finned sump on the transmission of my Chevy Express tow vehicle. On the hottest day in So Cal, the transmission drives at 100 degrees or less while towing a 22 foot trailer and going uphill tops off at 210 degrees. Money well spent. I kept the tires at 29" to aide in towing.

Did you have to add any extra trans fluid after installing the bigger cooler?