If everything is new and working correctly I would think you still have air in a line somewhere. I had a similar problem a few months ago on my '91. I bled the breaks in the proper order, got a nice flow each time from all valves, and still had break fade. I decided to bleed the whole system a 3rd time using new fluid. I bled each vale until fresh clean brake fluid came through the line. This did the trick, brake fade is gone.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed