Just wanted to bump this again since this also is why I came here, and Dan's post helped me. I could not find the adjusting info, even directly from identifix. All I could find was how to measure the disks where the shoes sit. Which doesn't help at all.
My pedal also goes pretty much all the way to the floor to get it to hold, but at least it does work. I might try it again tomorrow when the sun comes up, but at least it works now.
I have an '06 Express 3500. (and a silverado, and two impalas)