Don - I'm late to this thread. My Dad bought a zero turn mower when he retired (his expensive retirement gift). It was a Simplicity badged Ferris - a very nice machine. At the time, his house was nothing but steep hills. He had mowed with a JD lawn tractor for years and struggled with traction and side to side stability. The zero turn, he thought was the ticket. Lots of trees to mow around, with separate hydro motors at each wheel = positive traction, and a wide track. He got that zero turn on some of those hills and lost traction. Once the traction is gone, so is the steering. After a few uncontrolled plummets to the bottom of the hill, he sold it. As scary as that was, his biggest gripe was after almost 50 years of a steering wheel, the levers were hard to get use to. He bought a Simplicity Prestige and is a happy retiree.
OTOH, my Brother mows with a zero turn where he works. He uses an Xmark (which I think Toro owns). He loves it - fast mower too.
I've seen several lawns mowed that looked steep with zero turns, but the ones I've seen up close doing it were Grasshopper zero turns. They had some kind of funky chevron tread rear tires. So the hill traction problem might be solved with a combination of tires and weight.
One thing I really like that a lot of these zero turns do is stripe the grass. Do you have a striping kit for your Toro? Also, having owned Wheelhorse tractors (which were bought and destroyed by Toro IMHO), the one thing the do well is with documentation online - parts, manuals and repair manuals.
FWIW, I also think these new heavy duty zero turns are the reason we don't have serious garden tractors by every manufacturer today. The heavy duty that went into Cub Cadet and other makes back in the day is still present - just in a zero turn.
How's that for a long post?
Good luck with your zero turn mower.