I have a 98 K1500. I want to add a leaf to the rear springs for hauling a slide in camper.?

Well, since you have the entire leaf packs from another truck, you can 'tune' your rear suspension to what you need.

I would start with one of the shorter springs from the middle of the pack, then go from there. Add a longer leaf for a little more stiffness. You may need a longer centering pin/bolt (that holds the pack together) since your adding another leaf. It depends on how many leaves your truck has (they came from the factory with 2 different amounts one had 1 more leaf than the other)

Air bag helper kit is what I'd go with. You can adjust the pressure to what yo need and let it out when not hauling. If you are saying you have an extra set of springs to make a custom stack of springs that is trial and error to come up with a good combo.

You could also add a product called SuperSprings. They just add on to your existing leaf springs. They'll only affect the suspension under a load - this way you won't end up with a rougher ride.

Here's a link:

http://www.tsetruckstuff.com/page/tsetruck/ctgy/su...

If you want stonger leaf springs replace yours with springs from a K2500 hd. Adding a spring from the extra set that you have will not make them stronger it will just change your curb height.