The rear disks didn't come out until they GMT800 chassis came in '99. Those were only on the 1/2 and light 3/4 (semi float) ton trucks. The Tahoe and Suburban got them in '00, and the C6P 3/4 ton (full float) and 1 tons got them in '01.Side note, the C6P 3/4 ton and 1 ton trucks used 2 different fear axles, depending on which engine was specified. Base trucks with the 6.0 gas engine got an updated version of the 14 bolt 10.5 ring gear diff that's been used since '73, Duramax and 8.1 gas trucks got an 11.5" ring gear rearend, whcih I beleive may have previously been used in the 3500HD 1.5 ton GMT 400 body trucks.
