Brakes locking up!

Seek professional guidance. What was the concern that caused you to replace the master cylinder? Your description is something I cannot understand. The brake booster itself could be failing, causing the vacuum pressure to not release. But it's a wild guess, and with such an important safety component, I would strongly advice professional guidance from a shop near you. There are so many questions and concerns since repairs were attempted -- and we don't know the quality of the workmanship, parts, or even correctness of components used. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops