92 Break Pedal Travel too long?

I have a suspicion my power booster may not be doing it's job.

The break pedal travels close to the floor. I had all of the lines changed and blead. All new rear wheel cylinders. Absolutely, no leaks.

The Master had been swaped out for a new remanufactured but not the power booster.

The pedal does push back when the ABS comes into play. Found out the winter when slidding on the ice.

Is this a booster issue and if so is it doesn't seem difficult to replace but I'm not sure as to how the booster works...so a little theory of operation would be appreciated.

Thanks