the brakes go to the floor it sounds like it has air in the brakes makes a air sucking sound/hissing sound when i press an hold the brake it sounds like the engine wants to stall. it barely stops i tried replacing the master cylinder, an it is still doing it, i bled the brakes an its still doing it. 1993 buick regal custom 3.8 , 63k miles. i just had a new brake line put in it because it blew out on me before this, a new caliper an new back brakes. the front they said need changed within a 1000 miles, the lines arent leaking old or anything, theres still full oil in the resevoir.

 

From what you describe , it sounds like the is a problem with the vacuum brake booster .
If you remove the vacuum hose to the booster and plug it does the engine perform as it should?
With no vacuum assist because the booster is not functioning correctly, the brakes can require extra effort to stop the vehicle.