vacuum loss during braking on 1992 Chevrolet Suburban 1500

I have had a spongy brake pedal and have a vacuum loss when I brake. I have replaced the master cylinder and bled the lines including the control module, 4WAL. I can still hear a squishing sound coming out the power booster boot. If I cover the end of the boot where the shaft comes out, I have a firmer pedal. Could that be my vacuum loss? Should I replace the power booster.

Definitely sounds like a vacuum booster problem.