2007 Camry v6 hissing noise when brakes pressed and brake go to the floor

So I have a 2007 Camry V6 automatic with close to 200000 miles on it.  
Recently the check engine light came on along with VSC lights.  I checked
the ODB2 codes and got P0171 and P0174.  Now, I have noticed a hissing
noise when I press the brake pedal and, with continued pressure, the brakes
go all the way to the floor.  You almost have to pump the brakes to get the
vehicle to stop normally.  I checked and found not leaks in the brake lines or
around the reservoir.  The brake fluid level has stayed at max.  What could
be causing this issue?  The only work that I have done recently is change the
alternator, but I doubt that is the cause of this problem.  Any suggestions or
guidance would be greatly appreciated.