This dodge of my friends is starting to aggravate the *** out of me. The engine physically will not heat up higher than 180 degrees measured at the thermostat. The rad is blocked off, new 195 thermostat, decent water pump flow, we go and wump it in the bush and it won't overheat, its around -5 degrees to -10 here in ontario. Anybody with any idea at all. The only other thing is a high flow air intake, straight piped exhaust and a bummed cat converter. *** its better on gas right now but no heat. Any help would be greatly appreciated.  

Check your heater core take both hoses off fillone up with water blow it out with an air hose about 120 psi. Repeat this process from heater core hose to heater core hose. Back and forth until water pours out of the top heater core hose. My truck only runs at 145 degrees and my heater hose going back to radiator was cold compared to the one going to the heater core. try it any ? let me know.  

running water through the heater core is a good idea but can give faulty info. it looks like full flow but its not. took us two weeks to find that out. replace the core.