Do you have lots of flow through the tank on the radiator when the thermostat opens, look in the tank with the radiator cap removed, (be sure to remove the radiator cap with the engine cold and then bring the engine to operating temp while the cap is removed) and are you sure the water pump is correct because there is one for the SOHC and the DOHC and they look almost alike except for the sprocket.

Have you power flushed the block with the thermostat removed? There may be a lot of gunk settled in the block.

2009 Sorento LX, 4x4, V6, Auto, Red