I just bought a 550 and have some rather hilly terrain to mow. It has wheel weights on the rear but I'm not sure if the tires are filled or not. Is it considered a &quot;stable&quot; tractor? I go up and down as much as possible but there are a few places where I'll have to be sideways on the hill. A friend mowed it last time with an International 300 and had no problems. How will the 550 compare?