1999 kobelco sk150 ymu2043 swing problems

I have a 1999 kobelco sk150 IV, the swing is weak until u either boom in or out or boom up, it will swing normal while using other functions, just trying to get pointed it right direction! My operator said it went back to working normal with him for about an hour and half then next day started same thing! I have already changed fluids and filters. Any ideas would be appreciated. Thanks