More updates:

1) What is considered the normal range for ECT? No consensus. Probably 190-205 depending on your thermostat rating.


2) At what point would you stop the truck and wait for it to cool down? No consensus. I have set my personal number at 229 or greater - as long as there was no audible boiling or overflow. If there was boiling or overflow I would immediately stop the truck.

3) Could this be caused by me having the heater core hoses hooked up backwards? No. It does not matter how the heater core is connected on a 1993 TBI truck. There is not a heater control valve and there is no flow restriction in the heater core. My particular problem was that vortec heads were blocking internal coolant passages that allowed for coolant to bypass around the thermostat. The small amount of bypass flow is needed to prevent local hot spots in the cylinder heads.