The steering will be easier when it is moving. Jack up the nose of the tractor and see if it still steers hard with the front tires off the ground. If it still steers hard check the steering box. Some one may have tightened the gears trying to get rid of steering wheel play. If problem goes away after jacking then its a matter of manwell steering.
Let us know what you find out.
Let us know what you find out.