i have now idea about your specific tractor
everyone else is getting on ya about a lever or a knob. that is between your legs / under the seat. or right or left of the seat. and i am also going to jump on the band wagon. and say double check your levers / knobs. some levers / knobs. control amount of fluid that goes to 3pt hitch. (kinda like slowly turning on/off water faucet on kitchen sink) other knobs/levers, may put 3pt hitch into float, or return it to a given position to other. this happens to many folks including myself. leg hits something a hand or what not. and i never realize it, till all of a sudden i go to do something, and like AAAAHHH?!?! what is going on.
your statement of after it is warmed up. i have to assume when you first start tractor up when it has been seating over night. and you work the 3pt hitch it raises and lower just like normal speed.
i am wondering if you have a valve sticking open, or spring or seals in valve bad. or if one of your cylinders seals are getting to a point of once warmed up and expanding some. allowing fluid to by pass around. but there really is no way to "test" things, without gauges. and hooking up gauges in different locations as you try moving levers about. and then move gauges and try again.
any local tractor dealership / repair place for tractors, should have gauges on hand they can test the hydraulics with. gauges can get rather expensive, that can read higher 2000 to 3000PSI (pending on your specs of tractor). and if you haven't went through basics of checking levers/knobs. and take to dealer for a woops. ya out of $$$!
