1973 Jeep Wagoneer with sagging rear end?

I have a 1973 Jeep Wagoneer with the usual sagging rear end. I think the leaf springs are shot, I put brand new shocks on it all the way around, and it seems that every time I hit a bump or somthing like a speed bump, it feels as if the rear end all but bottoms out. It has a noticiable sag in the rear looking at it from a distance. I am wanting to put something more heavy duty underneath it, like leaf springs from a 3/4 ton pickup. I am not sure if this is doable or not, but the suspension they put on those Wagoneers are not the greatest. Any ideas on how to beef up the suspension without spending a lot of money? I dont want to lift it if I dont have to, at least not stick it way up in the air. A little clearance is ok but i am not looking to lift it. Thanks for the help!