i am going to get smacked across the face, but seems like ya going pretty good overkill for 1/2 acre yard.
have you tried every filling the rear tires with fluid to get you some extra weight in the rear end, and get some better traction? weight in tires also helps some by getting COG (center of gravity) for the tractor a tad lower, so less chance of flipping it over on a hill.
swamping out rear tires for say R4 or R1 style tires that have ribs in them to grab the dirt, on a riding lawn mower is a tad overkill, and you will more likely get better luck with "tire chains" on rear tires.
the up hill battle you face is both, a light weight machine, and tires that will not give you much traction. and you will most likely face same issue no matter what machine you end up with.
granted 4x4 / MFWD will help, but overall fill tires up with some fluid, and see about chains for rear tires, maybe even wheel weights.
if the engine simply does not have enough HP to spin the tires in all condition (( you are loosing traction)) then its not a HP issue but traction issue.
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BAH just forget some riding lawn mowers, you may need to get "wheel / rim spacers" do to not enough clearance :/ it might be possible to swap real wheels, so you get a wider mowing machine and give you enough inside clearance for chains. (( its all in the rims, and how much offset the rims have, that can allow for this))