Glad to see you're getting it worked out.
I do a good deal of my own work, but I'm not a mechanic, but let me take a stab at what happened and anyone feel free to correct me. During the process of changing the rear brake lines, lot's of air entered the system. Probably even made it into the fronts since the MC reservoir went low. So trying to bleed the brakes from the rear only, and then looking for the pedal to be firm isn't going to happen until all four corners are completely bled. Once all four wheels are bled, THEN the pedal should get firm. Am I on the right track?
1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor