I would definitely suggest not working the tractor as hard. As soon as a cylinder stops moving don't keep leaning on the control for more than a second or so. If you're trying to get thru a stubborn root I go at it with on and off motion and try to change the angle. Backhoe's are very tough on the tractor so it's wise to be a gentle as you can. If you're lifting up the front of the tractor while using the hoe you're putting a huge amount to strain on the tractor as an example. I will push my hoe to pull out stumps but I like to ease the pressure onto what I'm digging, kind of feel it out, I never jamb a control full on from neutral, always ease into it.
Cylinders and hoses will get warm or even hot to touch under a lot of usage, that's normal (I know my splitter cylinder gets hot enough you can't touch that without gloves for example.) but it shouldn't impact your loader valve operation. Possibly the valve needs to be serviced/cleaned. Or maybe the hydraulic fluid needs to be changed out. (These are just guesses - I've not idea why the loader valve would become stiff, I just know that's not normal.)
Maybe post that question in the hydraulic section on the forum there's people there that really know hydraulic stuff well beyond my basic understanding.
E.
