The F-450 / 550 Chassis-cabs are unchanged when it comes to the load capacity, tires/wheels, etc. The F-450 pickups are the ones that changed.
On another note, I wouldn't be surprised to see Ford phase out the F-350 DRW and make the F-350 an SRW only truck since they've done this to the F-450 pickup. Now the only real advantage the 450 has over the 350 DRW is towing capacity so why keep both? The payload is virtually the same.