A radiator is simply a liquid-to-air heat exchanger. Overheating is the result of not enough radiator, and/or not enough airflow. Does the engine overheat at idle, or does it only happen out on the road? Try using a laser heat sensor gun to see what the temperature at the bottom of the radiator is as the coolant goes back to the water pump. If you're not getting at least 40-50 degrees of temperature drop from top to bottom, you're going to need a more efficient radiator.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!