Brake issue with my new setup

[wolffcub]

Converted the 52 with a disk kit back in the day and ran drums in the rear. Things appeared to run ok even though the truck was never 100% done and only test driven. Now i changed out my rear end and the new one has disk brakes. The disk disk setup never worked with the other proportioning valve from the disk drum setup so i bought the WILWOOD ADJUSTABLE COMBINATION PROPORTIONING VALVE. After installing that the brakes were always super spongy after bleeding at least half a dozen times.

Went out and bought a new master cylinder today that i know was based on a disk disk setup and im still getting this poor feeling pedal at times. When i say at times i mean this.........when the valve dial is set full counterclockwise (less rear brake) the pedal feels perfect, as i turn in the pedal the spongy feel comes back. To me it does not seem normal this happening when allowing more pressure to the rear

Any ideas?