brake bleeding issues

[shelby987]

this is not for one of our trucks, but I am sure it should apply....I had to replace the rear wheel cylinders on my 93 oldsmobile....and for some reason I can't seem to get pedal feel back to where it should be. I replaced the rear wheel cylinders, the front rotors, and pads and shoes on all four corners.....I have bleed the system started at the rr, lr, fr, and the fl corners of the car....and the pedal still goes almost all the way to the floor.....any suggestions?
I wasn't sure if I needed to bleed the fronts, but after just bleeding the rears, the pedal was on the floor, so I went back and did all four corners.
The problem, when the car is off, the pedal feels firm after initial bleeding.....when I start the car....i get one or two good firm steps on the brakes.....then its right to the floor......best and brightest.....help would be appreciated!