The master cyl went out (went all the way to the floor). I had a rebuilt put in. Afterwords, the brake pedel was not as high off the floor as before. Seems to stop okay, but when I press a little harder at the stop light, I hear a squishing sound as the peddle sinks lower, but not all the way to the floor. Is this master cyl working correctly?

I don't remember hearing it before, but I may not have been listening for it. What explains the squishing sound?

You may have gotten a defective rebuilt. It sounds like it is leaking internally. Did you have a shop install it?

have you bleed the brakes anytime you change a master cylinder you need to bench bleed then bleed the brakes!!

Yep, make sure person who replaced the master cylinder bench bled it first, then bled the braking system.

-Rod