Engine not performing

[Cartwright74C]

So I have a 2013 ram 1500 tradesman V6. I recently replaced my transmission heater and after doing so my engine began to over heat so I topped off coolant and replaced the thermostat then the engine began to run below operating temp thought maybe a bad thermostat returned and replaced same issue so I replaced the ect sensor same issue. I have engine code P0128. My truck runs cold when driving and then overheats while idling because the fans won’t kick on. Any thoughts?

 

[crash68]

unless the water pump is failing it sounds like the system is air bound.
What was the reason for the TMU replacement?

 

[Cartwright74C]

Tranny was overheating so that’s why I replaced it I was hitting 260 after replaced it runs about 200, I tried burping the system but I’ve never had issues burping a cooling system like on this truck I’ll get air to bubble out and then it just eventually boils over but I believe I got all the air out, a water pump would cause it to run cold when driving? It’s just weird because it’s cold when driving then over heats at idle and the fans don’t kick on. Frustrated because I don’t like paying people to do repairs I always do all my repairs so I’m annoyed I can’t figure it out