Make sure the electric radiator fan is going on at appropriate temperatures to cool the coolant down in the radiator. Make sure it's connected up and so on and so forth. Sometimes, sediment builds up in the coolant passages, causing the overheating to occur. Consider having it flushed out and replaced the coolant with a 50/50 mixture of antifreeze to water. If pure antifreeze was used, instead of a 50/50 mixture, it can cause an overheat condition to occur as well.

Make sure all the air is out of the system ...