If you swap you lines does the problem move to the other direction? If you disconnect the lines and remove the cyl. and try shifting the carriage manually with a pry bar does it bind up in one direction? With lines disconnected, plug one line and hook up a pressure gauge to the other. Check your readings both directions/both lines and are they the same? If so then you have a bad cyl. If the readings are differnt and there is no binding in the carriage you have a valve problem.