Desperately need help with Brakes

[Short68Chevy]

Good evening.
I am completely stumped. I have replaced about everything in the Brake system. I have completely new rear brakes and springs, four new wheel cylinders, new rubber hoses, a new Master Cylinder, new distribution block and a new line kit. I have everything in and tightened up. The master cylinder was properly bench bleed. I now have two issues. First no matter how long we pump I can not get any pressure at the rear wheels. I can get fluid out but it is just a trickle. I have looked at every connection and I do not see/feel any spots that are leaking. I don't know what I am doing wrong. The other issue is that I am able to pump the brakes and get pressure in the front. But when I try to bleed them I have fluid coming out for two tries then nothing and I loose the pedal. If I switch wheels or wait a few minutes I am able to build up pressure aging but it goes away when I try and bleed again. I need any suggestions you all can give me. This is the last thing I need to do before I can get my truck on the road again.
Thanks in advance for you help.
Jeff