Why would the shock act as a pogo stick on flat surface? I was thinking if it only did that hop on braking pumps, or on rough conditions, then maybe you would need to decrease your rebound, or increase your damping(I think). But since it happens on flat black top, I would suspect maybe an unbalanced rim. It could be so out of wack, or maybe have a flat spot, that when you go, it just bounces you. So when your bike is on a stand, spin the rear tire and see if it wobbles or moves up or down, etc. If it does, it needs to be trued. So check out the tire being untrue first.