You probably already know this, but for the benefit of others that may read this thread, always remember when driving HST that lifting your foot off the pedal increases power (and reduces speed) just like downshifting. It is natural to want to push harder on the "go" pedal when the tractor starts to bog down a bit and that is exactly the opposite of what needs to happen. Of course the gear ranges are there to match the work at hand, and be careful changing ranges on a hill, an unintended stop in the netural position can have a less than desirable effect. Since the brake pedals are often where you dont expect htem to be, and on HST tractors not used as often, a freely rolling tractor (probably backward) can get a little intersting and a quick turn of the steering wheel can get even more fun resulting in unscheduled ROPS and seatbelt testing.
as for the OP question, I feel the DK40SE has a realatively low center of gravety (for a tractor, lousy as a sports car). filling the tires with ballast will lower the CG even more.