Back in 2008, the Society of Automotive Engineers (SAE) came up with a new standard for light-duty pickup tow ratings. Called J2807, the standard would simplify the testing methods for determining the max tow weight a light-duty pickup could handle. The standard was to be implemented in the 2013 model year, but it wasn't. Ford in 2012 surprised everyone by saying it would not adopt the new standard for the 2013 F-150 and would wait till the 2015 redesign. GM and Ram followed suit there after. The reasoning behind this? J2807 would have likely lowered the tow ratings and that wasn't something you really wanted to market. Toyota was the only manufacturer to do it and saw its towing ratings on the Tundra drop 400 pounds.
Now two out of those three implement the standard for 2015. Automotive News reports that Ford and Ram will adopt J2807 for the 2015 model year. As for GM, a spokesman says "when the other two major manufacturers move, we will move at that time."
Source: Automotive News (Subscription Required)