> 
> Open up the rear heater valve, and the front one too.
> 
> Now, when the temp gauge starts climbing turn both heater blower's on.
> 
> If the gauge drops, this would leave me to believe that the radiator is
> the culprit.
> 
> By doing this your adding more cooling area , and this means that the
> radiator is partially plugged.
> 
> Simple, quick, test.
> 

The heater circuit is independent of the thermostat, while the radiator is 
not. Turning on the heater fans bringing the temp down can also indicate a 
bad thermostat. Cheaper and easier to replace than a radiator. Probably 
better to start there.