I have run into a very similar issue on a new to me tractor but without the temperature component. Very sluggish and intermittent operation on power steering, PTO, aux hydraulic lines and 3-point arms. I replaced the pump anyway as I had already planned to do so and thus had one with no change. The supply hose looks great, but I found out that the fluid and filters are in fact old/of unknown age.
My current hope is that stirring up gunk plugged the filters and that a fluid and filter change will fix everything, but I am concerned about my next step if that doesn't get it done.