Quick check on my brakes after reading some posts here...

I press on my brake pedal and get a good firm pedal feel that seems to handle light and moderate stops fairly well. But when I press really hard on the pedal, as hard as I can even, the truck doesn't really get past a moderate stopping distance/power. The tires will never lock up either. The drums are adjusted a little bit tighter than spec, trying to get a little more oomph out of them. I'm thinking maybe my vacuum assist isn't helping out like it should. I pump up the pedal with out the engine running and start it but don't notice a drop in the pedal pressure. Should I be planning a hydrovac rebuild?

1955 Chevrolet 4400 1.5-Ton