Maybe it was one of those deals where you get so excited when it’s finally time that you trip over your own tongue?
It was either that or the most unique butt post EVER.
A classic case of unattended keyboard plus cat if I ever saw one.
I’m going to go with bad thermostat. It gets warm in stop and go driving, but cools off on the highway? The thermostat is stuck on the “open” position. (But yes, check the fluid levels).
I remember my Honda Civic replacing that every 2 years way back when. Friend of mine with a Detroit product was forever replacing that thermostat. Should be easy to check if it is open when cool or not. (Handy hint, check functionality to see it opens are needed by boiling it in a pot of water…)
The symptoms and the circumstance with which the problem started point strongly to just being low on coolant from not bleeding the system. Heater barely getting warm is a very strong indicator.