Baring having an engine stall and die on you, or transmission problems..  The problem on the "lumpy" ground and having a run-away is sliding on the straw. Either the standing straw or the straw after combining..  Yup,, dry conditions, and enough hill and a combine will slide sideways or slide down the hill. I've had it happen to me,, gets a little interesting and absolutely NOT the time or place to panic.  You've gotta keep your head level even if the ground isn't.  Get your header down, hit the override on the leveler and lean the sob into the hill as much as possible, and point the combine down hill at an angle that'll make a slow arc to the hill,, and use BOTH brakes g e n t l y.. If you've ever had it happen once,, you get the hang of it not so exciting the 2nd time.

You won't see many high cutters or overloaded grain tanks on hillside machines.