Hard brake pedal, no stopping power

Are the first-gen W-body power brake boosters prone to defects? Are they a common problem?

Background:

I did a search on "Booster" and got a bunch of hits; it seems the power brake boosters on the first-gen Luminas are not overly powerful--but--I don't see anyone who has claimed to fix poor stopping power with a simple booster R 'n' R. Folks upgrade to a newer, larger booster for "better" brakes, but that's not what I'm dealing with--I think.

What I'm dealing with is an extreme case. I have two 3.4 Luminas, a '92 and a '93. Both of them have poor stopping power, (the '93 is worse than the '92.) Both of them have working rear calipers, both of them have functioning emergency/parking brakes, both of them have vacuum to the boosters and booster check valves that hold vacuum. Both have firm pedals--no indication of air in the system. I have pressure to all four calipers on both cars as verified by my brake caliper pressure gauges. A hard stop will warm up all four rotors on either car. On glare ice, both cars will rattle the ABS, and the car is steer-able while stopping. Therefore, I believe the ABS is functioning properly.

How bad is it? On regular pavement/good traction, I can use BOTH FEET and ALL MY STRENGTH on the pedal, and the car glides to a stop. I CANNOT get the ABS to engage, the brakes don't grab hard enough to skid the tires. Normal, non-panic stopping seems to take more-than-expected effort; but it's not death-defying. I have replaced pads and rotors on the '92 with Z-E-R-O change in stopping power--although that did get rid of the shudder/pulsing of the warped rotors. I have never changed the pads on the '93; although that's in-the-works.

By comparison, my Dad's '98 Monte Carlo will stop with the slightest pressure from my big toe. There is a H-U-G-E difference in braking effort needed to stop between the Monte and either of my Luminas.

I have a rebuilt booster on order; I guess I'll find out if that was the problem in a couple of weeks...