I'm going with air pocket, or fan issues. Clutch fan or aftermarket? If aftermarket, not trying to sound stoopid or anything, but make sure it's not on backwards. I've done that before.
Ryan is talking about the radiator being clogged on the OUTSIDE, not internally. In other words, bugs, cat hair, dirt, etc etc get stuck on the outside of the radiator, blocking any air from flowing through it.
Didn't run over any squirrels lately did ya? hehehehehe