[GuyO]

Umm, if not hoses and shoes then it sounds like a proportioning valve not centering correctly forcing the rear to lock and the front to pull. If it were me I would go back to bleeding with new fluid. It sounds like you are very methodical and understand brakes and how important it is that the hoses must be lower than the bleeder so wire them down and let the air raise up. The prop valve must be clamped and the rubber button held in place (bleed the rear drivers first, then rear passeneger, then front passenger, then front driver). With the system free of debris, clean fluid and a centered prop valve you have elimated almost everything except for replacing the prop valve. Good luck. G.