Ok Bob, You mite have a problem finding info, the 5000 series did not come with tandem axles, my bet is they got installed along with the front drive axle. GMC Tandems started with the W5500 series. You mite want to be looking for a rockwell axle manual.
I just looked in my GMC Manuals for bigger truck and don't see your axles listed in them anywere.
