Eric,

The manufacturer specifies the MGVW which is the maximum gross vehicle weight. It is stamped on the plate that is probably on the driver's door pillar. From memory, the SD has a MGVW of something like 4550 lbs. Its empty weight is about 3650 thereby giving it a maximum payload of about 900 lbs. Now, if you go over this value will you damage any springs or shocks or suspension components? I highly doubt it. The value is set based upon safe handling and braking of a fully loaded vehicle. It is not set based upon the maximum static load that the suspension components can handle. If you had to move 1500 lbs., I'm sure that you could do it for a short distance at low speeds but you'd never get the manufacturer to tell you.