Contact Thermagasket @ 1-925-215-1211 and ask them. I had same problem with my 98 Northstar and they sold ma a part that takes 10 minutes to install using a knife/scissors and a screw driver. Stopped my car from overheating instantly. Northstar has built in problem, this fixes it.
Be care-full my radiator blew up and burnt me. I replaced Radiator, thermostat, and water pump. Timing belt is in the way so I replaced it too. OK Now
check your radiator. is it clean or does it need to be replaced? a simple cleaning cured my problem.
did you check the radiator or the head gasket?
check your fan clutch if its weak it will overheat
When the thermostat and radiator were replaced, coolant could have dripped into an electrical connector or a sensor could be disconnected or damaged. Check the temperature sensor and crankshaft sensors first.
you might want to check for a blown head gasket or a cracked head or block. espically if it loosing water out of the radiator with out leaking on the ground.
You need to check coolant temperature sensor and the water pump.
dose the electric fan run if not check the relay if it runs check the water pump
I would guess that the thermostat is not opening at the proper temperature. Once it does open proper circulation brings it down to the correct operating temperature. I think it should be replaced.
Try replacing the radiator fuse relay
Check the timing.
Try taking the thermostat out completely, then see if it still overheats. If so, your only other problem has to be a bubble in the system and it needs to be burped. Took me about an hour to get a stubborn air bubble out!