Thanks for the suggestion. I tried it, but it did not make a difference. Brake fluid came out, but the piston did not release.
I went back to the old calipers, cleaned them up a bit and reinstalled them as a test and they work correctly. I can only assume there is something wrong with the new calipers. What that is, I don’t know, but I guess I’ll take that up with Centric and see what they have to say about it.