Help ID rear axle

[mcmlxix]

I just picked up a 2008 Sierra RCSB and I need to do something with the rear axle. Its whining and I don't know the history on the truck...and I want to install a Detroit Truetrac but the application guide is somewhat lacking (read: I don't know what I have)...

I had a dealer print my RPO codes from the VIN. I have 3.73 gears (GT4) but no code for the G80 locking rear diff...

What I need to know is:
10 Bolt => 8" OR 8.5/8.6"
Spline => 27 or 30

I believe the Truetrac should be PN 913A481.

Also, look at the notes from Summit Racing and let me know your thoughts. I assume I need the LM603049 bearing and LM603012 race.

Notes:8.5/8.6 in. Eaton differentials require special bearings. For axles with small bearing bores (race O.D. of 2.89 in.), usually found on vehicles prior to 1999, bearing LM102949 and race LM102911 are required. For axles with large bearing bores (race O.D. of 3.06 in.), usually found on vehicles from 1999 to present, bearing LM603049 and race LM603012 are required.