HAD CHECK ENGINE LIGHT DIAGNOSED, WAS TOLD LOW COOLANT TEMP.

low operating temperatures is an indication of an air lock in the cooling system
gauges need the sender unit to be fully immersed in coolant to work but if they are not then the variable resistance material in the sender bulb cannot accurately relate to the coolant temperature
example if you have leak develop in a good system and you do not regularly scan your gauges like a good drive will do. it is possible that you will smell a dying engine yet when yo look at the gauge it will be reading cool to cold because the coolant has dropped to a point where the sender is no longer in contact with the coolant

Have you not googled your obd codes
& diagnosed them, to find a problem

No idea why you would do all you did

You always resolve code related issues first

The coolant temp should be 210 all the time

Sounds like your not looking at scan tool data
or following any factory trouble charts or actually
know what coolant temp is,your just assuming & not
doing the required testing to verify things

No heat or low heat in a water cooled engine is worthy of an immediate check as major damage to engine could be the result of continuing to drive it. Things to check:

These two things may cause no heat and possible not ever show as a problem on the temp gauge or temp warning light until far to late:
Low coolant/antifreeze level
Frozen coolant/antifreeze
Stuck thermostat

Other possibilities that may/may not show other signs of trouble as well:
Failing water pump (this would also explain some noise, typically like a grinding, scraping or bad bearing noise)
Slipping belt (Typically associated with the famous belt squealing or chirping noise)
Clogged radiator and/or heater core
Non-operating temperature control valve
Stuck thermostat

Hope this helps!

My guess would be the temp sensor has failed or is unplugged.
What is the trouble code stored in the computer ?

If the Check Engine light is coming on the computer is storing a code to let you know what the problem is. Have your computer scanned and you will probably find out what the problem is. The temperature gauge cannot work properly if the cooling system is leaking. The sending unit has to be in the coolant to work. If the coolant is low, the sending unit will not be in the coolant. If the coolant is leaking from around the radiator there has to be a radiator, radiator cap, or radiator hose leak.

If I understand you correctly, your temp gauge shows correct operating temperature, your blower fan blows air that you can feel with your hand from the right floor or dash outlet, but that air doesn't feel warm until you are moving?

If so, several possibilities come to mind. One is that your coolant level is low. Even though your temp gauge reads in the right range, the coolant level could be low enough that it doesn't reach the heater core until there is enough engine RPM to create more pressure from the water pump and force what coolant is there toward the heater core. Another possibility is that your heater controls are not able to do their job. A stuck flapper in the duct or a malfunction with the temperature control system could be causing the problem, and at 15-20 MPH there is enough air coming through the outside air vents to provide some heat.

I'd check the coolant level first, though. The other possibilities are more far-fetched.

the engine coolant tempurature sensor may be failing, the reason why truck stalls when light comes on is that the pcm thinks there is still a problem, then shuts down. after replacing sensor erase problem code with a obd2 scanner. if you do not have access to 1 you can go to any auto parts store and they will turn light off for free.

The only other thing that will cause too much pressure in the coolant system is a problem with the headgasket sorry to say...

this does not mean the sensor is defective, it most likely means the engine thermostat is stuck open and the engine is not running hot enough to satisfy the computers preset temp requirements for minimum eng operating temp.