Chevrolet Silverado 1500 Forum : “what kind of differential is in rear axle”

I found a whole thread on "Differential problems on 00' Silverado" on the Automotive Helper forums: http://www.automotivehelper.com/topic133181.htm. According to that thread, in your glovebox you should find a sticker with a bunch of 3-digit codes that specify type or gear ratio for your rear differential: G80=locking rear differential, GU2=2.73, GU4=3.08, GU6=3.42, GT4=3.73, GQ1=3.73, GT5=4.10. Hope that helps!