Thermostat
 

it’s been more than a month now without my work truck. It’s a 2015 ram 6.4L. The thermostat is the culprit. Dodge Ram does not have this simple part available and does not have an exact date for production or delivery. This is nuts.

They sell them at advance auto or other parts stores. Without knowing the exact model of your truck, I searched 2015 Ram 2500 Bighorn (since the 6.4 is not offered in the 1500) an came up with this:
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https://cimg7.ibsrv.net/gimg/dodgefo...d9b3e9ed87.jpg