Hi tlr, so several reasons for the thermostat change:

the engine oil, transmission oil and coolant are tied into the same radiator so everything then runs hot,
im running a cast iron big block which generates a ton of heat, this degrades the oil and kills bearings
any oil i put in looks vaporized when i change it and
i plan on towing my trailer with this truck so i want to try and run it as cool as possible.