What is the weak link for Chevy max tow ratings?

Viperpoker wrote:

Ram added an Aisin transmission to make their numbers go up. The engine also has increased from 800 to 930 ft lbs of torque.

Ram has had the Aisin and the 385hp/865lb-ft Cummins in 2013 until 2016 when they increased it to 900lb-ft. From 2013 to 2015 it was the same frame, trans, and engines yet miraculously it was able to tow over 30k all of the sudden in 2015 when they went J2807 compliant even though nothing changed on the truck from 2014-2015.