K/h caliper hanging up.

Ok, guess i'll get involved with this posting too.
From reading the original posters description i get the impression that he "just installed" the brakes.
If that's the case, and didn't rebuild the calipers that may have been sitting for years, then ya, calipers get stuck in their bores.
An initial rebuilding before installation, would have taken care of that problem from the git go.
Another problem that people always seem to overlook in binding, stuck, pistons, is that over decades of use,the pad where it rests on the main body of the caliper housing tends to develop divits and gouges in the casting.
You have to file them flat, all over again for the pad to retract when piston pressure is let off.
Other than that, 4 piston Kelsey Hayes disc brakes work well, and always have.