I personally don't like or use Autozone parts.
They have a high failure rate, even on new parts.
None of the retail shops I network with in this area will install Autozone
parts for you at any price (well, maybe at some price) :-)
NAPA is a good choice for parts if you don't use OEM.
You've eliminated the possiblility of bad fluid.
The whooshing you hear when you remove the vacuum line means the check valve
is working. It's function is to hold vacuum in the booster so if you have
engine failure while driving you should still be able to stop. You could
still have a bad booster even though it holds vacuum.
Since it seems you rear brakes aren't working correctly I would not replace
the booster at this point.
While you were bleeding brakes did you push pedal all the way to the floor?
You can damage a master cylinder by doing this and a new cylinder could be
bad. You may also have gotten air in the load proportioning valve and it's
preventing the rears from working correctly. Look for a way to bleed at the
valve, not sure how it's constructed so I can't advise on how.
I don't advise using vice grips or any other type of pliers on brake hoses,
it can damage the inner liner of the hose and cause problems.
You need to verify visually the brake components are working, both front and
rear, when you push pedal. On front is easy, on rear you can pull drum off
just enough to be able to see brake shoes work and verify they will stop the
rotation of drum. I suspect your problem is the rear not applying and
causing the fronts to take more work and wear faster than normal.
HTH, davidj92