Its your shocks bottomming out or your coils would be out of shape like the ones in the photo. Try removing the coils and reinstall the shocks. Jack the rear axle all the way up till your shocks are fully collapsed and you can see how far your bump stops need to be extended. 37Kicker makes extended bumpstops and might be interested in making a custom size if neccicary.
Also are your shocks the calmini shocks in the factory location?
Mike