The steering on an old car is comparable to brakes in importance and safety. I expect some debris has gotten into your pump when you changed the return hose or from the old hose. The power steering pump is a hydraulic pump which operates with close tolerances. Any small piece of debris will cause problems, such as rubber from a bad hose.
Buy a rebuilt pump and new return hose:
To satisfy your curiosity, spend the extra $7.00 for the core charge and disassemble the pump after installing another to see what was wrong. Good luck!