would it be beneficial or even possible to install a proportioning valve to increase the front bias? I'm not really sure how it would work with the ABS system.
It's not the proportioning valve that is the cause. It is that early model GM trucks had different braking systems, namely the front setup, that is very efficient. I have spoken to several service managers at varies GM dealers and all report the 00-03, but mainly 00-01 have braking systems that usually go over 100-200K with out needing front pads. The rear setup was the same and wears out like a typical brake system. I guess you could say they were over engineered! One ex GM manager said he hated turning people away that thought their brakes needed replacing. He stated most didn't believe the trucks could go that long with out replacing.