Several things must be looked at. You used a flush? That may have put a bunch of junk into the radiator top.
Remove radiator and reverse flush with a hose. Then check for vacuum leeks. That can make them run hot.

#1 the thermostat was dry for a time and may have become stuck closed. Replace T stat and gasket. $10.00
#2 There may be air in the system. Did you turn on the heater when running after filling it?
#3 Is the cap good? $6.00
#4 Is there a fan shroud? If not find one. The Montero has a metal one that will fit. Junk yard.
#5 Is there any Resistance to the fan clutch? If it spins free with zero resistance then it should be replaced. $25,00
#6 Check water pump for movement in the shaft. $40.00
#7 Radiator is plugged. $ 40.00
You can pick up parts from RockAuto.com if needed. We may even have a discount code you can use in the general dissuasion area.