2000 Chevy Astro Spongy Brake Pedal

I have put new disc brake pads on front and new brake shoes (drum) on rear. I have proven that the rear wheel cylinders work and do not leak and I have proven that the front calipers work and do not leak. I also have proven that I do not have any leaks at all ! The pedal is spongy and does not get an immediate braking response with the new brakes, and the pedal when continued pressure is applied slowly goes to floor unless I let go and reapply pressure it seemsto set back up. After 5-10 minutes the ABS light comes on and when I shut engine off and later restarts the ABS light is off untill it goes back on in 5-10 minutes. I know I should go to a garage and pay for them to read the ABS codes, but I was hoping someone out there has any ideas. I always try to able to do my own repairs when possible. Thanks signed: I Stop for Breaks