Disconnect pushrod from elev servo and see if it speeds up. While pushrod is disconnected would be a good time to check for binding too. IMO you would be better off using wall-wart to charge battery whenever you can but especially after such a long time. Charge battery pack and if possible check each sell as it runs down. Look for one cell that goes down too fast and may be bad. When in doubt - replace the battery as it is easier than repairing a plane.