I recently purchased a Kubota 7500 with a Wallenstein GX600 backhoe attachment. Every thing on the backhoe unit seems fine accept the upward control of the boom. It is impossible, most times, to bring it up slowly...to feather it. It only jerks up. This would be a huge problem when working in close spaces. We've checked that the flow control valves for up and down are clean. I'm curious if should try removing the valve spool. I have worked on air valve spools but never on hydraulic. Could it be there is contamination of some sort in there or is it possible a cylinder needs work? Every other motion on the hoe seems fine.