I hate to tell you this but a friend's 1650 did exactly the same thing and it turned out to be the hydraulic pump on the tractor . He first rebuilt the front steering cylinder but that did not fix the problem . THe first question I would have is what type of hydraulic pressure and volume do you have on the three point hitch and the remotes . Will the three point hitch quickly pick up something heavy like a round bale of hay and will the remotes quickly pick up an implement like a harrow ? If the answer is yes , that would seem to point away from a bad pump and more toward the front steering cylinder .
One additional aside here , my 1850 has a screw on it just above the steering column that when it is either turned all the way in or backed all the way out ( I can't remember which )the front wheels have no hydraulic resistance and the tires basically follow the land . I do not know if the 1650 came with this . You might want to check and see if you have this screw and see if it has somehow been changed .