Have you ever changed the hydraulic filter? Assuming that it has one, this could be the culprit. Another thing to check is that the beam is adequately lubricated and there is nothing putting drag on the cylinder as it retracts.

At base of valve that end lever does not hook to inside there detent balls and spring on end you can tighten spring uping pressure on spring will hold steel ball tighter on spool. Some have cover plug on end that can be removed and using a flat blade screwdriver to tighten are allen wrench of coarse over tightening will not pop out are over come the detent. Hydraulic pressure inside valve pulls spool out of detent. Taking back cover off and cleaning very important regrease detent parts. If need help hydraulic shop that rebuild jacks and cylinder can do this.

barbedwire.....good thoughts. filter and fluid changed very recently and I keep motor oil on the beam so no drag there (no more than normal, anyway)

gatorrider2.....I think I understand your advice. I'm off now to take a look at the valve. I may post back for other instructionsa if I can't figure out what you're talking about....Thanks....I'll let you both know outcome.