Keep in mind, the thermostat doesn't control how hot the engine runs. It only decides "when" water flows into the radiator. Did you take the gun with you and pull over and shoot the engine when it was running warmer to actually verify that it coincides with the gauge? If not, maybe take the gun with you next ride out. Also, go ahead and check the coolant level, belt tension and look at the front of the radiator for obstructions. It sounds like the fan is working properly.
