Overheating

When car RPMs rose while in racetrack mode, temperature started fluctuating from normal to hot back and forth. Changed thermostat four times, changed temperature sensor, changed radiator, changed water pump, and pully, flushed system twice after pouring head gasket sealer. Performed block test. No white smoke from exhaust and does not overheat at idle with A/C. At first there was no heat from the heater, but after a couple of flushes it blows hot again. Cars only start overheating after being driven around town for over 30- 45 minutes or on freeway over 80MPH it seems. Check engine light not on and no leaks anywhere and oil looks fine. Dealership recently forced me to bring in car to" update PCM or else I could not renew my registration and since then my car keeps not recognizing my key fob to unlock only to lock and constantly bings, key fob not detected since even while driving. My diagnostic reader (TOAD) shows the raw data going nuts and flying so fast on screen that it's almost blurry whereas before it would run through quickly with codes but was legible and spaced somewhat. I don't know what the heck to do. Please any suggestions? Thank you in advance.