Lots ov variables here, we need more info such as do you have a front end loader? Many tractors have the FEL plumbed into the system up near the hydraulic pump and the fluid must pass thru this to get to the 3PH. A restriction in this valve or the often used quick connect fittings that connect it to the tractor could be a problem. As mentioned many tractors use a valve to regulate the fluid flowing into the 3PH cyinder to control the speed(particularly the lowering speed) of the 3PH to keep heavy impliments from slamming into the ground. Does your box blade also go down slowly? If so, this could be the problem.