[yossarian19]

Originally Posted by roger55

I've got a 305 TPI engine with a 180 Stant thermostat that I can verify that it does open at 180...The fan switch turns the fan on at 190 and I've verified that. The truck has Vintage Air A/C and all the testing I've done is with it turned on and the ambient temperature at 95 degrees.
After some extended in-town driving, the water temperature runs at 192-196. Getting on the highway and running at 65MPH (2000 rpm), it will warm up to 210 after about 10 miles. I Transitioning back to in-town driving, the temperature will come back down to 192-196.

These aren't damaging temperatures but what concerns me is a hotter day maybe up to 106-110 and pulling a highway grade. With what I've got, I have no room for the extra heat those things would do.

After a re-read...
Y'know, your truck is actually performing exactly as I would expect it to with a 180* thermostat. Hop in a new truck and drive it around town for five minutes. It comes up to 210*. Now hitch a trailer to it and drive balls-out up a highway grade. It's probably still at 210*. If you swap the t-stat for a 180* you'll only decrease operating temperatures under low load conditions - and it will still find it's sweet spot at 210 under high load.

If I was still an auto mechanic and somebody came in asking me to diagnose this, I'd tell them "operating as designed"