Raise the mower deck when the wheels spin. That takes weight off the small diameter idlers/rollers and puts that weight onto the tractor wheels.
Add a weight box on back. I use an old deep cycle battery back there because I'm too cheap to buy bolt-on wheel weights.
Sears markets some re-branded husqvarna garder tractors with upgraded transaxles. The K46 can be found in units in the $1700 price range running a 24hp briggs, while the K66 units will run you around $2400 with a 27hp kohler ... you can figure more for the husqy. Easiest way to tell is lift the seat on your mower and look for the sticker on the bottom of the seat. Search on those in www.mytractorforum.com
K66 mower transaxle is much sought after by mower geeks. It is servicable, with filter, fan, and remote fill tank and optional differential lock. It is also capable of pulling ground engaging impliments like a plow or box blade, so you could also level the hill :-) Here is one on ebay for $250
personally the narrower tires have much better grip than the huge wide ones.
the wide tires on lawn tractors are so they don't leave tracks. skinny tires in dirt tend to leave ruts.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"