1. Cooling Fan(s), if equipped with two, one may not be working due to failed motor, or relay contacts/control windings open, or current limited so they are turning slow, or mechanical drag/brush failure, etc. You really need a graphing multimeter and current clamp to figure out the motor issues.
2. Radiator Restriction - Partial plugged - coolant look like mud? Gets warm after pulling off highway (A/C off before trying this)
3. Thermostat stuck partially open - check to see of one side of the valve retainer bracket has broken - common problem with Stant's crap the last 10 years.
CAREFULLY observe these items, and let me know.
Jeff