Time for more bleeding... Really.
Get a helper or install speed bleeders (one-way valves) and start bleeding from the passenger rear working forward to driver's front.
Have the helper open the bleeder, press down on the pedal, have the helper tighten the bleeder then release the pedal. Repeat until all you get is a solid stream with no bubbles or foam. Repeat on all wheels in the order indicated above.
Speed bleeders eliminate the need for a helper. Just open them up one at a time starting with passenger rear and pump until the flow is completely clear.
There is a slight possibility that the propotioning valve has died, but you can usually tell that because the case is covered with brake fluid and caked-on road dust.
I hope that this helps!