These gauges and sending units are not calibrated to NASA standards, check the actual temperature with an accurate thermometer of your choice. I know you flushed the sytem, I have used the radiator flush "Thermocure" with success. It does dissolve rust in the water jacket that is an insulator. I let the solvent sit in the system for days. For peace of mind, if you flushed the system again, replaced the clutch and waterpump, you'd be about $100 poorer. Is replacing a pump and clutch a bad idea? Well, how old are the parts in your rig? Both are items at the mercy of wear and time. You could go utterly crazy and do the hoses at the same time.