61suburban,

Mine ran near the thermostat temp...180&deg. I look at this from a very simple standpoint, if there is nothing mechanically wrong with the engine/tranny, then you should be able to spec a radiator that will cool the system, it's that simple.

The engine makes the heat and the radiator dumps the heat. If the system isn't controllable with thermostats, then the radiator isn't capable of dumping all the heat generated.

I know this doesn't answer your questions, but I think this is how the problem needs to be looked at.

That engine probably didn't overheat in its original application, why would this happen in a truck with a huge grill opening, and giant engine compartment?

Stuart