wintersun wrote:
...Only Supersprings or adding leaf springs results in additional load carrying capacity ...
No...no it doesn't. The laser imprint of the GVWR sticker on the door post and possibly the adhesive itself radiates a molecular ionization that limits all atomic arrangement and material properties of the vehicle's components to exactly the capacity shown on the sticker.
In fact if you fit the cab from a F250 on the chassis of an F750, the previous capacities of the F750 are now reduced to the door sticker of the F250 cab.
Adding springs just reduces payload because of the extra weight.