its all about class ratings. Why is the pickup F450 only 14k???
A manufacturer can slap any model name on any vehicle they want, and it doesn't have any legal effect on a vehicle's class rating. The fact that the Ford F450 pickup has a "4" in its model name does not make it a class 4. Note that Ram plays those games too, check out
this chart (I believe it may be 2011?). The 3500 SRW Chassis Cab lists a GVWR of 9,900 lbs, making it a class H (see
49 CFR § 565.15) or class 2b (see
49 CFR § 523.2). And similarly, a RAM 4500 with a GVWR of 16,500 is legally a class 5 truck.
But, even those are purely subjective; from
40 CFR 1037.801:
Gross axle weight rating (GAWR) means the value specified by the vehicle manufacturer as the maximum weight of a loaded axle or set of axles, consistent with good engineering judgment.
Gross combination weight rating (GCWR) means the value specified by the vehicle manufacturer as the maximum weight of a loaded vehicle and trailer, consistent with good engineering judgment. For example, compliance with SAE J2807 is generally considered to be consistent with good engineering judgment, especially for Class 3 and smaller vehicles.
Gross vehicle weight rating (GVWR) means the value specified by the vehicle manufacturer as the maximum design loaded weight of a single vehicle, consistent with good engineering judgment.
"Generally considered"? "Consistent with good engineering judgment"? Yeah, right.

It would not surprise me if truck makers are arbitrarily assigning GVWRs (tempered, of course, with "good engineering judgment") to specific vehicles to maximize profits based on the state rules where they sell the most trucks.
Don't get hung up on the model names and focus instead on the actual rating stickers.
Then...do what you want with it. It's your truck; and your liability.