First a question.
Does the coolant leave the system? Or does the gauge simply register hotter than you like? If the coolant does stay in the system the engine is NOT too hot.
So what makes an engine run hot? A too low temp thermostat will cause the FLOW thru the radiator to be so fast that the coolant cannot be cooled enough and slowly builds up temperature that can lead to boiling out the coolant.
A too large pulley on the coolant pump can slow the pump down and lead to low flow thru the engine.
The fan can have too few blades or turn too slow, causing low air movement thru the radiator.
Lastly I have seen poorly modified Jeep sixes overheat from retarded timing at hi-way speeds. Is the timing advance working as designed on that Chevy?
Big Jim