Replacing would depend on how it comes out... I had a few ideas.
But, no luck freeing it. It looks like the cage nut is this style Here
I think its welded to the bottom of the tube. But no hammer whacks are releasing the nut from it, even tried putting a jack on it and using the weight of the truck to break it loose, no dice. Thinking next move might be to lift bed and break it free from bottom of tube.
In the meantime, pulled bumper by removing the bumper trim... what a pain that was.