definatly could be a relief valve problem
could also be a bad spool in main lift section of control valve
also could be packing or safety valve in one of the outer cylinders
since fluid has to go through the outers to get to the freelift cylinder if there is a problem in one of the outer cylinders (usually the first one where fluid enters mast system) it can cause the whole system to drift down.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.