If the berm is at all what I envision from your description, I would never try to box blade it going uphill. With gravity as your helper you may be able to use the FEL to good efffect from the top side, at lest till the berm is reshaped enough to let you safely drive over it going down hill with the box blade engaged. Your safety is more important than the efficiency of the task. Let the dirt wind up where it will till after the berm is way better shaped then clean up the scattered dirt.
It is good operating practice to ALWAYS have your hand on the joystick if the FEL is loaded and not laying on the ground or very nearly so. If the tractor is moving and the FEL is loaded your hand SHALL be on the joy stick. You have power steering don't you? You can steer with one hand.
At the first sign of trouble or things don't seem right or stable, get the tractor stopped and the loaded FEL on the ground. Then think about the situation and resume if safe. I have never rolled a tractor but have been in every 2 wheel situation possible several times each. Sometimes it scared the snot out of me. Sometimes the bucket was empty but full, empty, or in between, lowering it to the ground immediately helped stabilize the tractor and prevented a roll over. A heavy box blade can be nearly as bad if it is hiked up in the air to yield a better departure angle.
It is amazing how much stability the tractor looses when you turn the wheels more than just a little bit, especially when the bucket is heavily loaded. I have a cab and Kubota prohibits loading the rear wheels but I have 3 sets of wheel weights and carry a 1300 lb box blade for
ballast when working with the FEL. Still the tractor has enough hydraulics to lift the rear in the air instead of picking up the bucket if the bucket is overloaded.
Oh, by the way... if the loaded bucket is in the air your hand should be permanently attached to the joystick with the thought ever present in your mind that you may have to INSTANTLY lower the bucket to the ground.
When working on a hill side go slower than you think is required and don't let familiarity lull you into a false sense of security. When you get a reasonable number of hours of experience then you can start to explore the edges of the safety envelope.
Like with us pilots,
there are bold tractor operators and
there are old tractor operators but
there are precious few OLD BOLD tractor operators.
Best to you, with care you should get 'er done safely.
Pat