Did some troubleshooting this morning. Ive determined that I don't think the thermostat is opening, let me know if you agree.
1. Confirmed no more air in system (best I could).
2. Filled reservoir tank to correct height (it was empty)
3. Let truck idle with radiator cap off and heat on.
4. Truck idled until it reached 206*
At this point the radiator overflowed out of the cap and all over the floor. The top hose measured 160*, the bottom hose was 110* and the thermostat housing was 150*.
This leads me to believe the thermostat is not opening correctly and is also probably getting stuck closed during the times it reaches 221*.
Something wrong with these numbers. 1st leave the rad cap on the radiator. The system needs pressure to operate right. If your dash is saying 206 and the thermostat housing is saying 160, what is the temp on the motor side of the thermostat, as in before the water goes through the T-stat. It should be 206 if your truck gauge is correct. If it isn't your sensor or gauge is defective.
If the Thermostat is not opening, then the Radiator should never have overflowed, otherwise where did the overflow coolant come from?
The cooling system in your truck is really pretty simple, it should not be anywhere near this difficult to figure out what is going on.
Simplified picture of how the coolant flows.