99 C2500 work truck strange problem

[alabbasi]

All, I'm hoping that I can get some help here. I'm working on a 99 C2500 work truck with the vortec 5.7 and vacuum brake booster. The brake pedal felt very low so I replaced with master cylinder with a delco replacement.

When bleeding the brakes, it seems like the pressure from the pedal is blowing fluid back into the reservoir rather than the other way and out of the bleeder. Getting to the point where the fluid is now very cloudy. I went through and bleed all four wheels following by the ABS pump using my scan tool.

I've never seen fluid getting pushed back to the master cylinder so I'm wondering if i got a bad part , or if something else failed down stream.

Any thoughts would be appreciated.