[JBRAVO383]

Has the water pump been replaces recently?

on my 85 There was a v-belt water pump on my 383 when i was running a serpentine set up. In-which a serpentine set up runs the opposite way a than a v-belt set up. But my temps were fluctuating 185-225 and when i would rev it up my upper radiator hose was being sucked shut.
This may not be your problem but just something to look into.