When discussing vehicle tow ratings, one point must be acknowledged... trucks today can tow more than ever before. Having said that, one must recognize that historically, truck manufacturers took some liberty with reality in determining tow ratings. It seems that competition, rather than physics often determined tow ratings.
Well that all changed with (Society of Automotive Engineers) standard SAE J2807. Finally, some ground rules were established for determining tow ratings so that for the first time on this planet, tow ratings of vehicles from different manufacturers could be compared.
SAE J2807 was initially published in 2008 (revised 2012), by the cooperation of the major truck manufacturers. However, initally only Toyota adopted the standard. It was rumored that GM would adopt the standard, but only if Ford did as well, and the circus began. Again, it seems that "one-up's-manship" between competitors was more important. In 2013, all of the truck manufacturers have promised adoption of the standard.
As of 2016, Ford, GM and RAM are publishing their tow ratings in compliance with J2807 (according to their 2016 towing guide brochures).
Interestingly enough, here are the tow ratings for my 2016 model year vehicle (J2807 compliant) with the same vehicle in the 2015 model year (not J2807 compliant):
So what changed between 2015 and 2016 that accounts for a loss of 2,400lbs in towing capcity? Certainly, there were a few minor changes between model years, but not anything to account for this difference. What changed is in 2016, GM started using SAE J2807 criteria in their brochure tow ratings.
SAE J2807 criteria:
It should be stated that the vehicle's actual weight must still not exceed the GVWR (Gross Vehicle Weight Rating), the trailer's weight not exceed it's GVWR, and the combined vehicle and trailer's weight not exceed the vehicles CGWR (Combined Gross Weight Rating). As well, the GAWR (Gross Axle Weight Rating) must be within their limits. This has always been the case. J2807 simply establishes a set of criteria for determining the MAXIMUM tow ratings within that criteria.
With the adoption of SAE J2807, consumers finally have a common yardstick they can use for determining the actual towing performance from the various vehicle manufacturers.