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After the parked and running test, did you check the coolant level to see if it had gone down? Not trying to be a jerk about it but maybe the problem is intermittent?
Radiator cap? Maybe pushing coolant to the overflow and "overflowing" then sucking the overflow reservoir dry after you shut it off? Bit of a stretch, but it has to be going somewhere. Pressures and temps higher when driving versus driveway? Smell coolant while driving?

If you have a mirror, look on the bottom side of the water pump to see if there is any coolant residue. Depending on how much/when it is leaking it can be evaporating off hot engine at higher rpm. Coolant leak might also be disguised a bit if hot coolant is picking up oil on the outside of engine and running down, seen that as well but maybe the outside of your engine is cleaner than mine![]()