Yeah, the first thing to do it take a hose to the ragiator. Go by a Do-it-yourself carwash and blast the radiator from the rear with the pressure hose. Pushing water through the fan blades makes it so that any junk collected in the front gets pushed out easily. To do a really good job you might have to take off the fan shroud. But becarefully with the high pressure hose under the hood. Don't direct it at any components that you don't have to, you don't want to get water under the distributer cap, inside of the brake reservior, or into any electrical connections.

Since the overheating happens at highspeeds and lowspeeds it probably isn't your fan clutch. So, the next step would probably having your engine power flushed. This will remove any obstructions that might impede flow and cooling power within the engine.

Hopefully between those two attempts your problem will be solved.