It is true that with many vehicles, the OEM tow package is rated higher. Most of this has to do with the upgraded accessories that are part of the OEM tow package, such as HD radiator, battery, wiring, trans cooler, gearing, tow-haul switch, springs, brakes, GVW, etc. You need to compare apples and oranges.
This is the strangest life I've ever known - J. Morrison
2015 Airstream International Serenity 27FB with ProPride
2011 Ford F150 Lariat Ecoboost V6 Turbo Gasser