Twice a year, I mow a pasture that has sections with a near 20% slope.
@ParkWhite suggested that you take time to practice. That's what I did.. After my 3rd mowing, I understood how to take the hills riding up/down rather than attempting to go across.
To help with the turns at the top, a FEL was added to the tractor to balance the weight of the 5' brush hog on the back. I learned that big wide circle turns is the way to go and if that cannot be done, then back down the hill. A tight turn tends to roll the tractor.
Slow is the answer on hills. This ain't no race to "gitter dun". Being alive when done mowing is a critical goal to me! It takes me 11-12 hours to mow this field.
And no, for this machine, I would not want a bigger brush hog.
A bigger tractor? Sure. But there is nothing wrong with this MF1533 for this job if one is willing to take it easy, choosing to live!