Took a few minutes and installed the Derale Performance Fluid Control Thermostat for the transmission coolers.
Info
HEREThe thermostat came with 4 each 3/8 NPT hose barbs-

The mount came with 4 allen head screws to mount the unit to the mount & 4 sheet metal screws to attach the mount to the truck-

I wrapped the threads with some teflon tape-

The hose barbs installed in the thermostat-

Then I mounted the thermostat to the bracket and the entire assy to the radiator support with the sheet metal screws-

The lines were cut , slipped over the barbs and secured with fuel injection clamps.
The 2 adel clamps were reused to secure the hoses. Complete setup before I installed the grill-

I took it into the mountains again and the temps were much more stable. I saw the trans temp climb more rapidly, and it climbed to 188 F in the long grade. On the way down (under no load & coasting) I saw 170F.
After leaving the expressway the temp stayed at 170 F around town.
Looks like the valve is working!