I replaced all calipers, brakes,and lines… I have had the car professional bleed…but i am still get poor brake pressure???
Did you replace the master cylinder?
If you stomp on the brakes (no other cars nearby of course) can you lock up any of the wheels?
Some power brakes have a spongy feel but still are effective in provided ample stopping power.
You either have a bad (although new) master cylinder. A leak in the power booster, these have a bladder inside and in an old car like yours can go bad. A leak in the vacuum lines to the power booster. Or, still have some air in the brake lines somewhere.
My grandfather had an early '60’s Pontiac Bonneville and the brake petal never seemed to get hard as you pushed it. The brakes would put you into the dashboard and windshield and had plenty of stopping power.
Did the car have a different petal feel and something has changed, or did you acquire the car with the brakes this way?