Wheelslip is nothing abnormal. Hell even Shay 9 has wheelslip under the high bridge if you open the throttle up too fast. whats surprising about the video is that they don't really seem to do anything about it other then drop sand. And from my experience, if sand does not work, shut down and apply the brakes, and try again. You let it go one like they did in the video, you break things. That how the Blue Peter was nearly destroyed, it experienced wheel slip, and it ran away on the crew, with the wheels turning at over 130 MPH, right up until all the valve linkage broke and they blew a cylinder head. The engineer tried to throw the engine into reverse, and the Wheel (not a bar in the UK) for the reverser shattered both his arms.