I think the "slope" in your question puts Zero-Turns out of the running, IMHO. I had the same issue as you: using a lawn tractor on a slope, any time there was even a bit of dampness, I'd rip up my lawn using my JD L130. I got a Kubota
BX2230 (along with the 1830, the 2230 is last year's model, replaced by the 1850/2350-- I got a great deal on last year's model, because the dealer had two leftovers he wanted to get rid of before the new models came in). There are places to find MSRP on Kubota online, but don't pay attention to those anyway. Unlike JD, whose dealers will generally stick close to MSRP (they have to, I am guessing), Kubota tractors are sold like cars, depends on the dealer, what you want, how willing he is to bargain with you. I paid less than 80% of MSRP on my Kubota (MSRP was $15,500, plus extras, and I paid $12,000).
For your price range, you might want to consider a Kubota
BX1500 or BX 1830 with a mid-mount mower. You'll get plenty of HP, 4WD and Differential Lock. I bought mine with "R4" tires (Ag design, but with Turf in mind). Others may say go with Turf tires. I disagree. On my hills, it is MUCH easier to navigate up the hills going slow with R4 tires, 4WD and, if necessary, Diff. lock, without ripping any lawn. The only time there is a track problem is in areas where the grass is weak to begin with, and it is wet.
The other nice thing about getting a subCUT, like a Kubota BX is that you'll have a tool that will last a very long time, better gas mileage (diesel), and it can do things your lawn tractor or ZTR could never do (with two acres, there WILL be times you want to transport stuff from one area to another, and on a hill, 4WD is essential). Also, you can use inexpensive 3rd party attachments with your subCUT (e.g. Aerator, seeder/fertilizer, roller, utility cart, toolbox, blades, etc).
One last thing, if you do get a tractor like a BX, be sure it has a suspended mower deck, not a ridgid one. My hills have rolls. If the mower deck was not suspended, but ridgid, I'd scalp my lawn all over the place. Also, the 60" mower deck, availalbe only for the
BX1850/2350 (newer model numbers) has a self-balancer in addition to the suspension system. Check it out.
There are lots of tractors in the BX 1850/2350 class, made by JD (the 2305), New Holland, Case, Agco, etc. I think those are the "big three" and a few others. I went with Kubota for a number of reasons explained in my review on the review pages. Basically, it was (to me) the best-built, best-handling, best sounding engine, at the best price, for what I wanted. No regrets here. Try them all out though, your mileage may differ, and its a big investment.