2004 GMC 3500 rear end size question

[67sss]

Thanks for the help! 11.5" it is. Just replaced inner and outer bearings, seals, parking brake pads and changed rear diff fluid. I seem to have a "bounce" coming from somewhere. Shocks are new all the way around. Wondering if the carrier bearing is starting to go out? The best way to describe the "bounce" is after going over a rough road, it seems like the truck suspension feels like I'm driving over washboard. Probably will replace the u-joints and the carrier bearing to see if that helps. Any other suggestions are appreciated.