Brake Pedal Slow Pressure Loss

I changed front & rear pads and rotors on a 2002 taurus wagon. Afterword I attempted to flush & bleed brake system. The pedal started to lose pressure. I then replaced Master Cylinder with one from local dealer (and re-bled). I still am loosing brake pressure and have no visable leaks. Any help would be greatly appreciated.

How are you bleeding them? What is your process?

I connect clear tube. One end to bleeder valve, the other submerged in bottle with brake fluid. I have someone press the brake, when it is down I momentarilly open the valve then close it. I repeated this about ten times each wheel. I start with right (passenger) rear, then left rear, then right front, then left front. I went all around three times. I never let fluid in resevoir go less then halfway without refilling.

I think that car has a cross bleeding sequence, RR,LF,LRRF try that first, Next, it is possible to get a bad M/C even new or Reman'd, Third thing I have seen, but cannot explain is that some brake pads don't always get hardened correctly and will sometimes give you brake fade if this is the case. Also if your rear hydraulics are proportioned by valve in rear it is imparative that you bleed with rear wheels on ground.