I think you overfilled the radiator and that the truck's cooling system was just finding it's correct level.
When cold, the coolant should just barely cover the radiator tubes.
Is your cooling system a zero pressure system?
My truck had a coolant recovery reservoir on it when I got it. I like it because I can fill the radiator to the very top and coolant doesn't spill on the ground during normal operation.
The reservoir rises about two inches when hot, and goes back down as the engine cools off. The truck operates at a steady 180 and has a 4 lb pressure cap.
I think you’re probably right.
One oddity of my cooling system, and it seems repeatable over multiple, intentional, over-fillings: It’s happy level is slightly ~below~ the top layer of tubes. I have a homemade puke tank and the puke tank has an outlet once it fills completely.
