Power Disc Brakes not working on hard stop?

I'm kind of going through the same issue. Took the 70 Dart out today, and wasn't happy with the stopping power at high speed. Small bolt, manual Kelsey Hayes brakes, 14" wheels. My plan of attack will be to scuff/clean the front rotors, and find the latest, greatest front pads. Then take off the rear wheels, and scuff the shoes and drums, and reinstall/adjust.

Somebody mentioned to you about glazed pads/rotors, and you looked right past it. Could be your problem. News pads, and a normal brake service.