I want peek performance out of my transmission, so I added a "big" cooler years ago. Worked pretty good in the summer, but was too cold in the winter. So I got a bigger cooler and added a 180°F Thermostat from Perma-Cool (part # 1060). I no longer use the radiators built in trans cooler.
Mounted the Thermostat on the right frame rail under the alternator
It has 2 IN & 2 OUT ports. I blocked the cooler IN port.
Hot fluid comes in the E1 port from the transmission
Cold fluid goes out the E2 port to the above trans filter
Hot fluid goes out the C1 port to the trans cooler
Got a bigger cooler now 11 X 11 X 1.5 stacked plate rated to 30,000 GVW.
Got a new filter mount that has 4 side ports, So I don't need any plumbing Tee's now.
1 IN port is for fluid from the Thermostat
1 IN Port is for fluid from the Cooler
1 OUT port send cool / clean fluid back to the transmission
1 OUT port is for the trans gauge temp sender