I am making the assumption that you have ehydro? Also that the fluid level is up on the "XXX", and colder temps/thicker fluid is not sluggish to start the day and fails to improve?
If the engine seems to be bogging causing the trouble, I'd look at air or fuel delivery issues, but it sounds like your hydraulic flow is restricted/gpm is low.
When you say you changed the inline filter, you disassembled the inline screen/strainer on the port side of the machine and brought the screen back to bright? If you have power beyond installed, there is similar screen in the back that may be blocked. How many hours are on the machine? Has it been prone to cavitation? Any fluid leaks?
