Power Disc Brakes not working on hard stop?

That's why I asked about bleeding the brakes post #7.

Did you pre-adjust the rear shoes to a slight drag?
Could be the slave cylinde(s)r are stuck or the rubber hose between the body and axle has collapsed.

Check the front calipers for symmetry, have someone "lightly"press the brake pedal while you observe the caliper for movement. The pads should come in contact with the rotor at the same time. Press full pedal,: are you getting equal movement, not favoring one pad or the other?