I understand the drum brakes are coming on the '05 3/4 and 1 ton trucks. That's just what I heard, don't know for sure.
As for the original question, you got me! I haven't heard of anyone wanting to go from disc to drum, only the opposite. I would first check with GM and see if the proportioning valve is working correctly. 70% of braking should be done by the front brakes and the rears should last longer. The next thing I would look into is going with softer pads in order for the pads to wear and not the disc rotor. Then, if you didn't know, DO NOT, i repeat, DO NOT get the rotors resurfaced each time you replace the brake pads. It's only necessary if the rotors have deep gouges in them.