What I did:
I have a 1997 GMC Jimmy that I replaced the power brake booster and rebuilt the rear drum brakes (new brake shoes, springs, and wheel cylinders). I bled the rear drums since I replaced the wheel cylinders. I did not have to remove any lines from the master cylinder in order to remove the power brake booster / install the new one so I did not bleed the front brakes. I also topped off the brake fluid in the master cylinder.
The problem:
When I took it for a test drive, every once in a while the brake pedal would stick to where I pushed it to and there would be a squealing kind of noise coming from the area of the brake booster. I took the car on about 5 test drives and every time it would do it at least once. Sometimes it would happen when I slam on the brakes and sometimes it wouldn't. Sometimes it would happen when I was just pressing regularly and again, other times it wouldn't. The easiest way I found to get the pedal to come back up to normal position was to put the car in park and pump the pedal.
My question:
What could be causing this? Is the power brake booster that I was sent defective or is it something else? Any suggestions or ideas would be greatly appreciated!