Q: Tundra 5.7L overheating on highway.

I purchased a 2011 tundra with the 5.7L V8 in May 2016, it had 45,000 miles on it at the time. From day one the engine coolant temperature gauge will fluctuate between 5/8 and 3/4 when going down the highway with the cruise set on level ground, however if I "mash" on the throttle going down the road and increase engine rpms the gauge falls back down right below halfway. This is occurs when at any period of prolonged constant speed, with or without the AC on. Driving around town the temp gauge remains right underneath halfway. I purchased an OBD2 reader and connected through my phone and when the temperature gauge is reading high it indicates right around 230F. However there is ZERO indication that my motor is running hot other than the temperature gauge and OBD2 sensor, no boiling over, no antifreeze smell, no fault codes, no decreased mpg, oil is clean and fresh throughout the entire vehicle, AC blows cold, Heater blows hot, no decreased coolant levels or leaks, no abnormal color

My car has 50000 miles.
My car has an automatic transmission.