Known overheat issues 4.7 RAM V8? EDIT FIXED

My neighbor bought a 4.7 1/2T Dodge plow truck recently, so no real history. It seems to overheat bad on the highway and I did warn him about plow blockage. They tried a new stat. Anybody familiar with "known" issues with this engine? Is there any tricks to filling them? I have not looked at it, he just called me. Heater works REALLY well he says. Bear in mind it's been COLD here high temps last two weeks in low 20's and teens this week.

I told him to try and figure if it is "really" overheating (feel around heads etc) try to find infra-red thermometer.
He said T stat changed things, I even mentioned maybe the new stat is defective
I can't see a rad blockage as it would seem the heater would block first, but ?? (These heaters have tiny passages)
Likely not a water pump or heater would not work "well"

Ideas?