Don't jump over a speed bump if you can. Pretty much any racing vehicle is going to do that over a speed bump. If you really want to do it, you are going to need to tinker with oil weights and probably substantially increase your rear ride height. If you are packing up and the back end kicks up without compressing at all, try decreasing oil weight or going to a larger holed piston. If you are driving through and brutally chassis slapping, go in the opposite direction.