I am having what seems to be high temp readings, at higher speeds IE interstate, temps are hovering around 210-220 & occasionaly will reach 230. I.ve replaced the thermostat twice, replaced the radiator, the original plastic fan had several cracks so I replaced the fan with an electric fan sutible for primary cooling, I've since adjusted the fan thermostat down so it runs anytime the ignition is on & still seeing these temps, gauge was also replaced with aftermarket electric gauge. no bubbles in coolant & no coolant loss. Any ideas? BTW, I drive this truck 40 miles 1 way to work everyday, has not ever shown signs of being overheated when I shut it off, no boil over or pressure being released etc.

 

What year 4.0l?
Ranger had 4.0l OHV engines from 1990 to 2000, the 4.0l SOHC engine from 2001 to 2012

 

Sorry Ron, 95 model, not SOHC.

 

What does the temp show after warm up and at idle?
Does temp increase at idle?
That would be a sign of water pump impeller blade issues, or Fan clutch, which you don't have

During highway driving overheating could be failing EGR system if you have one, EGR cools cylinders to prevent high NOx emissions
Lean condition causes cylinders to run hotter, usually you would get pinging/knocking when accelerating if that was the case.

Heater core blockage, often the heater core is used as the by-pass in cooling systems, if core starts to get clogged up the engine will run warmer.
If heater blows HOT air then probably not the issue, it would just blow luke warm if core was starting to be blocked
And you can always by-pass the core to test if that's the problem

If you have a 4 hose heater by-pass valve in the engine bay then it could be bad, allowing flow with heat selector on HOT but blocking flow back to water pump when selector is not at HOT