Floyd suggested a new engine, anything else to check before I go that
way? What's a rough cost of new engine?

I didn't suggest a new engine....that was JohnC. You may only have a
partial blockage and the engine may not be damaged. My overheat sensor
activates before the head gets to the boiling point, at least on the
outside. You can dribble water on it and it doesn't boil or steam when the
alarm starts. When the engine overheats to the point of making steam, I
wonder if it would be visible?
I haven't heard of the flushing device you mention, but it couldn't hurt.
Let me know if it works to clear your engine, assuming that's the problem.