I would bet you have air getting sucked back in past one of the rubber cups you did not replace. I had a 1950 DeSoto years ago that I rebuilt the front Wheel cylinders (I honed them and put kits in them, new rubber!) and one of them would suck air in (top on driver side). I had brakes all day long, just fine. After sittin overnight, I had to pump them to get a pedal. If I opened the bleeder on that cylinder, and pushed the pedal down to the floor once, it let all the air out and then I had brakes the rest of the day till it st overnight! I wold replace all of the rubber cups or even the wheel cylinders.
