looking to add some payload to my 2002 sierra 2500HD. have a 8ft salter in the back and seems to drop the rear a little. what would be better supersprings or add a leaf

 

I personally like my air bags

 

Supersprings are overloads that are progressive. Where you plan a constant load having a leaf added to your current pack will work just as well and be a heck of a lot cheaper. I paid $140 including the leaf springs for my last truck and adding Supersprings to my new 2500HD is going to cost $450 for the springs alone.