Is the Radiator cooling fan spinning? If this fan does not spin it will cause the engine to overheat and we need to figure out why it does not spin. Have you checked to see if the water pump is providing sufficient water flow? One thing you can do is, with the motor cold so you don't burn yourself, (BE VERY CAREFUL NOT TO INJURE YOURSELF BY TOUCHING THE MOVING ENGINE COOLING FAN) grab the radiator hose coming from the water pump to the radiator and squeeze the hose firmly (but do not collapse the hose) while the engine is idling so you can feel the water flow, have a helper raise the engine rpm and see if water flow increases, water flow should be much higher at higher engine rpm, if no change in the "feel" of the hose can be felt, the water pump impeller has most likely internally failed due to corrosion and the water pump needs to be replaced. If you cannot tell which hose is coming from the water pump, perform the check on both hoses.
Please check the two things I asked you about and let me know if you need any further assistance.
The cooling fan spins fine and the water pump was just replaced
Excellent. Was the water pump replaced earlier in this same process of trying to correct the overheating issue, I.E. was the motor overheating before replacing the water pump?
Does the vehicle have a radiator cap on the radiator, or is the cap mounted on an external coolant reservoir(overflow tank)? The next thing you would want to check is for a possible head gasket leak or cylinder head leak. What you want to do it let the vehicle cool off, then once cool, remove the radiator cap. watch the coolant for bubbles and smell for fuel smells coming from the radiator, neither should be present. If no bubbles or fuel vapors are coming from the radiator cap, the next step is to replace the radiator cap
Are we 100% sure the thermostat is facing the correct direction, if installed backwards the motor will overheat
If the thermostat is installed correctly, and there are no bubbles/no fuel vapor smells in radiator and the radiator cap replacement does not fix it, you have a clogged radiator or engine block or cylinder head
thermostat correct, no leaks, no smell
system was completely flushed
The system being flushed doesn't eliminate the possibility of there being a blockage in the system, or repair it, if one is present. There could still be buildup in the system that lowers the systems ability to move coolant and dissipate heat enough to cause overheating. A faulty radiator cap is much more likely than a clogged engine block/cylinder head/radiator though. I recommend replacing the radiator cap
did you need further assistance?