I was plowing my driveway today and the steering started to get hard and then easy if turned harder. I guess you could say it was skipping.Felt like low oil but was up on gauge glass. Tractor has 300 hrs and is Kept in heated garage. Trans oil and filters changed at 200 hrs. plow down and wheels off ground acts the same. Dont think its the pump but could test pressure. Dont know how to test steering box..Machine has no leaks and pump and box look pretty heavy duty to wear out so fast. If anyone has seen a problem like this I could use advise Thanks