Don't know if this helps, but (my experiences only):
1. Master cylinder push rod was not releasing fully when installed, needed adjustment (my 57 truck)
2. Flexible front brake lines that go to the caliper, collapsing (this is a common problem with JK Jeep Wranglers. I had to replace left and right).
They looked fine externally (30K on the Jeep), but replacing them worked.
Not sure this is true, but someone suggested that pressing the brake (fluid) overcomes the collapsed line, but there is not not enough pressure
upon release to overcome the collapsed line, hence sticking calipers.
Just some thoughts to possibly spur additional ideas.
don
