I don't think its a vacuum or canister issue. The pedal operates freely and power assist feels right. It's just on a hard stop I seem to run out of pedal which limits the pressure to the brake. I'm hopeful adjusting push rod will help. Will advise when I've been able to adjust and test.
Some good replies to your question, but I would like to add one more. Have you changed out your rear brake line to axle (rubber), if not it can be soft and expanding while putting pressure on them.