Cat c12 engine temp

I’ve owned the truck since 04. It’s an 2001. It has not had this happen before. Even the other day when it got into the upper 50’s it wouldn’t get above 175 when driving along. Just today actually I was bobtailing and it wouldn’t break 125. I am guessing it’s faulty thermostats. Not sure really what else it could be. It’s definitely not an electrical issue as far as sensors or gauge. It’s mechanical. Thermostats not properly closing would have to be the only thing allowing that coolant to circulate in effect cooling it down as it runs itself through the radiator and back through the engine.