If you feel the push rod is adjusted correctly, then take off one line at a time at each wheel. Put the end of the line in a empty soda bottle. Fill the master resovior. Have a helper push down on the pedal. Watch the force of the fluid and mark the volume of one pedal push. Do this to each wheel. Start with an empty bottle each wheel.

If each wheel is not consistent, back track.

BTW, is there a proportionating valve in this system by any chance ?.
If so, you may have to start before that point. It should be just after the M.C. some where.

A rebuilt M.C. is my first suspect. But it could be ok if you prove it as I just explained.