So are these rated to haul up to 50% more then stock ? If so that puts the 1500 close to 3000lbs instead of the 1600lbs it is rated for.
Thanks for posting pictures and the info.
HD rear springs can increase payload. However you will start running into limitations with other items on the truck, such as the tires, wheels, rear axle & differential and brakes. Obviously tires and wheels are easy to upgrade. So this leaves the rear axle and brakes.
IHMO HD rear springs should be looked at as something that allows the truck to better manage a load, and not necessarily increase the truck's load rating.
IIRC, the rear axle on the 1500 is rated for a maximum of 3900 pounds. You must subtract the truck weight from that 3900. Even given this conservative rating, putting 3000 pounds into the bed of a 1500 is asking for trouble.