Brake travel

Start with the simple stuff. Adjust the rear brakes up until it is TOUGH to turn the wheels. Take a short drive around the block, apply and release the brakes several times, leaving several seconds, say, 15-30 sec if you can between brake applications. Then come back jack up the rear and recheck the rears, tighten them up some more if they have become easier. This is just for testing. See if the pedal "comes up." If not, or very little, you may still have air.

You may have a mismatch between cylinder size, caliper piston size, and master cyl. bore. A smaller master and larger cylinders makes the pedal travel more, but gives you more braking force. The opposite is true with bore sizes reversed

Does the pedal feel fairly hard? Judging that is a lot tougher with a booster