Master cylinder was leaking! Changed the master cylinder, bled the brakes and reverse pressure bleed! Break pedal is really stiff and isn’t stopping very good! Checked the vacuum line and it’s working! What could be the issue? Thanks for the help!!!

 

i think you have to power bleed the system you can do it with a proper disnostic tool or by making a switch and wiring to starter and remove fuel relay to power the abs system of that braking system
watch the videos on atlantic british or just search

 

Brake pedal being very stiff and poor stopping power is classic vacuum leak. Check that your brake booster isn't leaking where it connects to the new master cylinder.

 

power bleeding might be strongly suggested but is certainly not required in my experience. mollusc is on the right track with a vacuum leak.

 

Op said he checked vaccum line and it was working

 

Vacuum line is "working" is very vague. Doesn't mean that the booster isn't leaking. That's different from checking the vacuum line.

 

How do I check for a vacuum leak?

 

Pull your MC out of the booster again, without disconnecting the brake lines. I bet your pushrod dropped down and is not pushing in the MC correctly.