Brake pedal travel issue.....Need help

[94 RT/10 Black MAMBA]

My brake pedal travel varies. Most of the time it's fine. But on about one out three applications it travels a lot farther (twice as far, but not to the floor). I changed the master cylinder but that didn't change anything.

Any ideas?

 

[carguy07]

Brake fluid boiling? Do you have headers? I would bleed them either way.