Durango Brakes Won't Bleed

Bought an 01 Durango RT a while back. It's rough, but it was cheap. We had to replace the front calipers because one locked up, basically had simple project turn into a super long, super painful project, but it's mostly unrelated. After we did the front brakes, the pedal was never really back, it worked but had way to much travel. Finally got around to fixing the pedal, replaced the back brake cylinders and all the hardware back there. Bled and bled and bled. No pedal. Replaced the master cylinder. Bench bled, and then bled and bled and bled. No pedal. The car has rear abs only, not all wheel abs as far as we can tell. We've put something like a gallon of fluid through this and it just wont bleed. Any ideas?
Does it have abs on the front or rear? Had a similar issue with a late model Jeep. Air was getting stuck in the ABS module. Fought it for a long time before I finally got it figured out. Also had a 97 dakota, which I imagine is similar to your 99 Durango, but it didnt give me any fits when bleeding brakes. Besides the dumb @$$ combo of metric bubble flare AND standard brake fittings on the same truck