hey there, the guys who posted above are correct, the shocks aren't made to carry load, they control they way which your suspension loads and unloads due to the strain on them and the way which the suspension travels, however if you have helper springs and they are installed correctly then you add carrying capicity when you springs are loaded, don't forget that adding shackles slightly changes your leaf spring geomtry can causes them to work a bit differently although this isn't significant enough,
I added and i recommend all explorer owners to do is to add a leaf to your pack, I ordered the kit from Summit and I couldn't be happier ! the stance is much better the truck handles loads better and it rides better because don't forget when your carrier ( king) leaf is worn down from age the weight of the rig is on the helper and load leafs they don't reflex the same way,
so add a leaf is the way to go, other than changing your leaf packs, the job is a pain in the butt but something you can handles in the driveway with basic tools
good luck