Ram has the same tranny and Cummins before they went to the 2013 with 3.42 gears. What they did was improve cooling in both the tranny and CTD. I'm guessing they did some tuning for the DEF as well. That was the downfall and the need for 3.73-4.10 gears before. Just look at the tow ratings pre 2013. Take my 2500 ST CC LB 4x4 for example. 
3.42=9500
3.73=12,500
4.10=14,500
Jump to 2013
3.42=17,300
The 2013 has the same frame as the 2012. For 2014 it got the improved version. 
Payload only went up 300lbs over the 2012 for 2013.