Sylvan,

First you need to check hydraulic oil for contamination, water, dirt or burnt. At the bottom of the motor is the lowering valve. Should have a red **** that you can turn to lower the mast manually. Also it has wires going to it for lowering with the switch. Raise mast about ten feet, then have someone else open the manual lowering valve to see if the mast comes down faster. If not suspect lowering valve has restriction. You may need to inspect the cylinders for velocity valve issues. These are inside the fitting where the hydraulic hoses connect. You can install a regular fitting and see if the mast travels faster. This would indicate a failed velocity fuse. The only other problem would be a damaged cylinder. Good Luck.