Wecome to our Forum. There are a lot of very knowlegable people here and you will get some good advice.
I can't help you with the shocks or air bags but with the money you are throwing at it I think you should move up to a dulley. You will have a wider footprint for stability, you can lower the tire pressure for a better ride and get it down on the overload springs to tighten it up.
I put the Kelderman system on a 91 Dodge and as you say they are spendy. I did it because my wife has a bad back and the ride was killing her. The Kelderman sure helped. My present Dodge 3500 rides better than the 91 W/Kelderman. It has a better suspension and I use less tire pressure. By the book 45 lbs will carry more than the axle rating but with the camper I use 55 lbs.
'01 3500 Ram QC HO 6sp. BD Exhaust Brake