C20 Burb Rear Springs

[MAC71]

I have a spring issue that I am looking for some thoughts on. This is a 72 C20 Suburban with big block and a dana 60. When I bought the Suburban about 7 years age it had a rather smooth even ride. Shortly after getting it I jacked it up and discovered that both rear springs were broken, as in the differential swung away from the truck and only the shocks and track arm were holding up the differential. I ordered heavy stock height C20 spring set from LMC truck, but with those springs the truck is really bouncy. I have tried 4 different types of shocks. The best shock so far has been some heavy duty Rancho shocks. I then ordered a rear set of springs from year one, but that made it even more bouncy. I am now thinking that the springs are to stiff and the shocks just can not control the springs and was thinking of trying some C10 springs. I was wondering if any one had any ideas?