Gehl 4500 Skid Steer Boom/Lift arm weak erratic

[r8f1k]

Just installed a professionally rebuilt lift cylinder on the left side. Now, once in a while the boom will rise VERY slowly and if you let go of the handle the boom will drop right away. It will do this over and over until you move the skid steer or shake the bucket. Then, it will work fine for quite a while. Did I get something in the system? Dirt, flakes, etc? Do I pull the relief valve and clean it? Is it the check plug? Spool problem? Clean fluid, full system, doesn't matter if the skid steer is hot or cold. Any thoughts?