S10 Blazer brake issue

I have a 1987 S10 Blazer was a 2.8, 700R4. When I bought the truck the rear brakes were not working, I looked everything over and things looked good. Adjusted the brakes and they still were not working I could turn the wheels with the brakes applied on jack stands. I since have replaced both wheel cylinders, new shoes, drums, and hardware. Still not working, I have re bled all four (4) wheels and still not working like they should.

The P.O has replaced the line from the proportioning valve to the rear hose.

Anyone have a suggestion on where I look next ? There is no emergency brake cables or linkage to interfere with the brakes

A deteriorating hose can exhibit that behavior. It would also be helpful to investigate the prop valve and master cylinder, since that's about all there is left of the system.

Well I ordered a new hose today so we will try this before swapping out the master cylinder.