What might cause a 1999 Pontiac Montana to overheat you flushed the radiator and changed the radiator hose What else?
Thermostat, water pump, defective cooling fan, or cooling fan thermo switch. The coolant system needs to be bleed so that all the air is removed. There are two bleed off valves located that need to be losened until all the air is removed from system. The owner's manual shows where the bleeder valves are located.