Ford F450 goes J2807

Quote :

For customers who require no-compromise towing capability, the 2015 Ford F-450 Super Duty Class 3 pickup boasts the highest rating of any pickup truck in the United States – 31,200 pounds, measured using the Society of Automotive Engineers J2807 standard
F-450 Super Duty towing capability is 2,200 pounds greater than its closest competitor’s crew cab 4x4 pickup truck
Ford will rate 2015 F-Series Super Duty maximum payload using base curb weight, aligning its payload rating practices with other manufacturers to make it easier for customers to compare vehicles
Ford reaffirms the undisputed heavy-duty towing leadership of the 2015 Ford F-450 Super Duty Class 3 pickup at 31,200 pounds after testing using the Society of Automotive Engineers J2807 standard.

SAE J2807 establishes tow vehicle performance requirements against certain performance criteria to determine a truck’s maximum trailer tow rating. Ford is a founding member of the J2807 committee, which includes other truck and trailer manufacturers.

“We leave no doubt with customers that the F-450 pickup truck has best-in-class towing of 31,200 pounds – whether tested using our own internal towing standards or SAE J2807,” said Raj Nair, Ford group vice president, Global Product Development.

2015 Ford F-450 upgrades
Ford improved the 2015 F-450 pickup by giving it a more capable version of the F-350 frame, plus a more capable suspension and 19.5-inch wheels and tires to enable its best-in-class towing.

The F-450 pickup is available exclusively as a crew cab 4x4. The truck’s J2807-certified maximum tow rating is 2,200 pounds greater than its closest competitor’s crew cab 4x4 pickup.

More here
https://media.ford.com/content/fordmedia/fna/us/en/news/2014/09/02/ultimate-towing-machine-2015-ford-f-450-rated-best-in-class.html

So on Fords own site they confirm the F-450 is a class IV truck and at the same time claim best in class when comparing to a class III. I'm still confused.