Is there a vacuum booster mounted behind the master cylinder, or a Hydrovac somewhere along the frame, usually on the driver's side behind the cab? Either way, it sounds like you've got a failed booster. Did you just get the bleeder screws changed, or the complete wheel cylinders?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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