Truck's got Power Brake issues (disc/drum)

[CochinoFilipino]

Her brakes don't feel right. When I apply them they work okay, but as the pedal travels, it sinks down midway and I have to apply more pressure to continue stopping.

I bled the the brakes. That didn't help at all.

I'm thinking I've got a vacuum leak somewhere.

Can I hook up a vacuum pump and gauge to the booster to test it? How much vacuum should I pull to test it? How long should it hold?

How much vacuum should I see coming from the manifold? And how do i check that? Disconnect the booster, or T' into the line?

Thanks,