I have a 2001 GMC Denali and have the same problem as well. Unfortunately for me, I tow a 28ft travel trailer and when camping on a hill, i'm really concerned about not having an Ebrake. Right now I just chock the wheels.
I just came inside after changing the back brakes, both the disc and the parking brake. After putting on brand new pads, I thought to myself there has to be something I am doing wrong when it still did not work. Well after reading here I am not the only one that has this issue.
I looked all over for an adjustment for the ebrake but found nothing. I am going to take both wheels back off and adjust the dial as far as it can go without binding on the rotor and see how that goes. It's a shame you pay this much for a vehicle and it does not have an ebrake. No wonder everyone is going with an import now.
As you can see I'm pretty pissed about this whole thing since I depend on my ebrakes and it seems there is nothing you can do. I am also thinking about buying new rotors since the older ones may be too worn in now. We'll see.
If this does not work, I'll post up and try to start a class action lawsuit, I'm sure there are a lot more out there that have these same issues.
Anthony