Next time you use the joystick, remove the boot and watch the wobble unit to see if it is doing what your think it should be doing. How loose/sloppy is it, and is the spool moving in and out equally.
A hyd gage is a valuable tool to let you see what the hyd system is doing in terms of, the pressure for any hyd action.
You know there is a relief pressure setting on the loader valve, that protects the hyd pump.
So when you go to full extend or retract and hold it there, the pressure should register the relief pressure.
If you see no pressure when you move the lift part of the joystick, that tells you the flow is not there for the cyl to develop the pressure.
That is a gear pump on your tractor, and will try and pump as long as the tractor is running.
With all valves in neutral, the fluid just flows through each valve in a series flow path to tank.
If the hyd jerk around, there is probably air in the hyd system, and it will normally purge itself.
The air could be sucked in from a leak in the suction hose.