Just a suggestion......bring the engine up to operating temperature.......TURN IT OFF.....and then run the palm of your hand over the inner finned surface of the radiator.....trying to find SPOTS that are cooler than the surrounding area. Cooler spots will indicate areas that are clogged up and you'll need to seek out a good radiator shop. An infared thermometer would make it easier but the ole "palm" can also work. The hot water flows into the top of the radiator and cools as it decends.
You didn't mention anything about your engine.....6 or 8....but if by chance it's an 8 you'll more than likely need a good fan shroud and if it's a replacement 8 in a 6 cylinder truck you need to make sure that the fan is oriented high on the radiator. The more info you can provide will get you specific info to cure your issue.
Dave
