Wanting to say that there were going to be three different rear ends(not gears) matching each of the new engines?
May be wrong on that as it was info from when they were announcing them.
But this is current GM media for the K2xx 6.2L set up.
The available 6.2L EcoTec3 V-8 is the most powerful engine offered in the light-duty segment, with 420 horsepower and 460 lb-ft of torque. Like other EcoTec3 engines, it combines proven performance with advanced fuel-saving technologies, seamlessly switching to four cylinders to improve efficiency in light-load driving
The available Max Trailering Package includes a 9.76-inch rear axle, heavy-duty rear springs, revised shock tuning for increased control, enhanced cooling, and an integrated trailer brake controller. Also included is the G80 locking rear differential, a trailer hitch, and bumper-mounted four- and seven-pin connectors
Sierra’s standard 4.3L EcoTec3 V-6 and available 5.3L EcoTec3 V-8 also will offer significant towing capability for 2015, with maximum available trailer weight ratings of 7,600 pounds for the V-6 and 11,200 pounds for the 5.3L.
http://media.gm.com/media/us/en/gmc/news.detail.html/content/Pages/news/us/en/2014/Jun/0619-gmc-sierra1500.html