Your truck is almost 20 years old and you springs probably are too. You said it had a big gooseneck hitch in it so you may not know what kind of load was on it most of it's life. I would start at a good spring shop. I think you are going to want to ad at least one leaf to each side before you start adding aftermarket suspension items. From your pics it looks like your front end may be going up when the camper is on it. If you can't get to a scale at least measure the wheel well opening above the front tire with and with out the camper to see if it is going up or down this can have a big effect on your handling.
I have a 2001 ram 2500 ext cab 2wd gas truck. With the stock suspension my truck did not sag as much as yours. My camper weighs 2540 lbs. I do have the camper pkg with the overload spring but when it is just sitting it does not touch. I guess my point is when comparing to mine your springs are either very worn or your camper is a lot heavier than mine I am guessing a little of both.