In 2003 Dodge switched to AAM axles. In 03-04 2500's came with either a 10. 5 or a 11. 5 axle. If it was a SO motor it had a 10. 5, HO's came with the 11. 5. In 2004. 5 when Dodge when the Cummins 600 was released and was a 50 state motor all diesels have the 11. 5, 2500 or 3500. Now the only rig the 10. 5 comes in is a 1500 Mega, or 2500 Hemi.
The 11. 5 is a seriously strong rear end, something like 33% stronger than the GM 14 bolt FF, which has always been regarded as a hefty unit.