Back end hopping after new Coils and Shocks

[Stinkfist]

I bought a 72 longbox off of a kid this winter. He chopped it too low for my taste. Lowered via cut coils with the original 72 shocks. (shocks were just for show It was a definate hack job, but since this is my first old truck I'm not sure what else he screwed with.

Purchased some ST 2/3 drop springs and some cheap stock shocks just to get it on the road. Ride height is perfect for me, but now the back end hops on any bumps in the road. It takes about three or four bounces before leveling out. With any load in the box, it will bottom out two of the four hops.

If I push the box down in the middle of the endgate, the shocks seem to respond as expected. Any force down on either corner of the box makes the truck rock side-to-side like crazy. Stepping into the box feels like getting into a boat.

Any ideas on what I should do? I've read that you can flip the shock mounts to use the stock sized shocks, but most only do that with a 4" drop. Better shocks? I thought the cheap ones would at least make it drivable. Upgrade swaybars from 73-80? Can the control arms condition make any difference?

Thanks for any help you can provide.