Verify the bore of the master cylinder. My guess is that it is 1 1/8". Install a smaller bore master cylinder to increase line pressure. If all else is good, that will solve your problem. Dropping down 1/16" in bore size makes a very noticeable change in pedal feel. If it is as hard of pedal as you describe, you might consider going to a 1" bore diameter. You will increase pedal travel and increase line pressure.