Your not plumbing it through the radiator and then through the aftermarket cooler are you mike?
I am or it wouldn't get warm enough in winter. In fact the factory hookup to the cooler is straight from the stock trans line.
The other is stock, cut, flared and then as you can see the hose connects from that to the cooler.
Running around town it stays between 120 to 130. Towing in summer 165, on the long grades in the desert in Washington 180ish turning 3800 to 4500 rpm running at 65mph. That is a combined weight of about 15,600lbs scaled.
The larger cooler kept it cool longer and cooled off much quicker than the stock and previous aftermarket cooler I had.
Stock cooler VS first aftermarket cooler. These are tiny compared to 40K trucool
Most 6.0 guys run it just like this because you just run the stock lines.