I've hesitated to comment as I am a relative newbie around here.. lurking for only 3 years. Learned a lot in that time. We mow 15-20 degree slopes on our 15 acre meadow. 1st year, lots of seat pucker owing to the slopes and not knowing the land. (We'll not mention grapevines on a bank sliding the tractor sideways into a creek)
It didn't help that there was no front weight on the machine pulling a 650lb bush hog. Learned real fast that one makes very long motions at the top of the hill - loops if you will. 2nd year, we added a FEL to our machine. Oh, that felt a whole bunch better. That's how we run now still doing the big loops.
The wheels are not filled. We have not seen a reason to do so. Not sure it would make a big difference on these hills but I've heard all the thoughts on doing so.
We run in 4WD always. I had one instance that first year where the dummy in the seat allowed the tractor to start downhill - not in gear. Total fail on my part... and quite the learning experience with the hog pushing the tractor forward. I got it under control.. but... had to run back to the house for a change of pants.
At 200+hours now, I am beginning to get the right feel of what I can and what I should not do. Mowing slopes takes practice and thinking about how to run the machine up and down those slopes. The more practice I get, the more comfortable I get.
Being an engineer, I choose the route that works well and then stick with that program every year...
Every time I start a new piece of land, which I have not mowed prior, I go super slow, taking what I have learned here and in the seat, making the best decisions I can make. Still, every piece of land offers surprises in the Blue Mountains of Virginia.
This summer, I am supposed to train a newbie. I worry about him rolling the tractor.
Thanks for all the advice... I find this forum immensely helpful.