(I have used this answer on several questions for chevy truck brake issues)
I have a 97 suburban, so I believe things are very similar. I too have replaced lines on this truck and spent hours of time and over a gallon of fluid trying to get it bled correctly. A couple things that I've learned and have helped.
Bench bleed the master. Remove the lines, install short lines, and have them go back to the reservoir on the master. Pump until no bubbles.
Bench bleed the ABS. Same as bench bleeding the master. I didn't try this, but I think it would have really helped.
When bleeding - Open the bleeder, push the pedal down, close the bleeder, release the pedal. This will help from air getting trapped.
A couple methods I've used:
Normal pump bleeding. Never quite got it right. I wasn't closing the bleeders in between pumps though.
Pressure bleeding - apply pressure to the master cylinder reservoir to push fluid through. Might had worked had the top been able to seal well, but it ended up just making a big mess.
Vacuum bleeding - apply vacuum at the bleeder. Be sure to use a ton of Teflon tape so you don't suck air from around the threads.
Reverse bleeding - Push fluid from the bleeder back through to the master.
I ended up modifying some bleeders by cutting the tip off so I could screw it all the way down to ensure no air would get past the threads. Used a ton of Teflon tape. Vacuum bleed until I purged the line, reverse bleed, install original bleeder, vacuum bleed until I don't see bubbles.
I think the reverse bleeding helps get the bubbles out near the master/abs where there is a long drop. The bubbles want to go up, and normal methods are trying to push them down. I might had had good success with bench bleeding the ABS first also.
You should also note, at least on my truck, part of the process is to have the dealer run an automated bleed on the ABS system. This takes a very specific scan tool. I tried several of my cousin's professional Snap-On scan tools, and they were not able to do the ABS bleed.