Bad booster?

Just got done instaling a 97 dual diaphram booster and MC on my son's 91 XJ. We bled the brakes and tried to test the brakes. The first thing I noticed was a loud hissing noise from under the dash and the pedal didn't feel right either. I tried to pump the brakes a little and found a lot of fade whenholding the brake. The peddle would not return quickly after releasing pressure.

So what say you? Bad booster or bad booster and master cylinder.