Curtis plow with up/down hydraulic problem

Hi all, I purchased my RTV900 complete with the curtis plow that uses the hydraulic control for the dump box. I find it is difficult to control the plow hight and I'm either taking chunks of gravel or leaving too much snow. First day I even broke one of the brand new stock shoes. I tried putting 2 adjustable line throttle valves on the cylinder to slow it down, but it didn't really help as I think the flows are so low.
Does anyone have any suggestions on how I can slow the system operation?

Curtis plow with up/down hydraulic problem