Do you have plenty of oil in the tank when it gets up that high? Sometimes if theirs only an inch or so over the pump and motor when it's at the top the suction from the pump and the oil bypassing in the tank causes turbulence and the pump can suck air causing it to bounce. I'm not sure packings would be next on my list. The tight packings I've had usually cause a hard initial up start or a bounce in the down level or a really abrupt down start. Have you tried putting it down on the springs to resync the pistons? And you can try some maxton or cat hydro oil additive too I you think it might still be packing related. It's cheaper then doing a packing if the customer doesn't want to pay.. hopefully something here helps
