It's an ACT S/S with heavy duty PP
I put it in when the engine and tranny were out.

I bled it a while back, and it was fine. Now today I went to start it up again, and the pedal shot to the floor and didn't come back up. I can pump the pedal with my hand and it will regain its resistance after some time, but then it will lose it again after a few more pumps. I'm certain it was bled correctly, could it be a bad slave or master cylinder?

 

It's a hydraulic problem. Check the fluid line for leaks. If there aren't any, replace both cylinders (they should always be replaced in pairs).

 

Ok, ordered both as well as a SS clutch line from mazdatrix today. Hopefully that will fix it.