Try bleeding the brakes with the master cyl. cover off. That's what i was doing wrong with my '81 Dodge truck and it solved all of the bleeding problems completely! Now the brakes are very good feeling and work properly.
I was ready to burn it to the ground i got so mad at it, and as usual, it turned out to be something simple!
Man, was i choked at myself after that, but relieved.
Tom.