This is the one I got
Amazon.com: Detroit Locker 913A555 Trutrac...EDIT: I think I got the passenger car version on accident, so don't get that one!
Here's some general info
http://www.drivetrainshop.com/GM_12_Bolt_s/105.htm
The one for truck rearends:
Amazon.com: Detroit Locker 913A315 Trutrac...
Now, the website says this is only for 3.73 and up gears so if you want to run shorter gears (as I do -- 3.42) then you might be out of luck.
http://www.differentials.com/uncateg...-differentials