My Ford 600 hydraulic lift arms would only raise about 1/4 of the range after sitting over winter. I lifted them all the way up and cycled the lift lever a few times. After that I had a full range of motion and a strong lift. The problem is now that when I put a load on it it initially lifts it fine, but slowly drifts down until the load almost touches the ground then it raises quickly back to the top. It will do this continuously as long as rpms are above idle. Any suggestions?