I can vouch for what Brett says. I have the Auburn limited slip, and it works very well in snow. It is much tighter than the stock unit that I had in my Ranger. We just had a decent snow fall here last week, and it performed superbly. Since I just installed it a few months ago, I took it out and put it to the test. Even with the original Firestones, the rear end would dig in quickly.
Brett is good on the price as well, although I paid about $250 to have it installed (they put new bearings on the differential). If you are on a tight budget, you may opt to just rebuild the original. I don't know if you can install extra clutches to tighten up the stock limited slip or not, but if you can, by all means do it. Just keep in mind that the traction-lok will not last as long as the Auburn.
If you do opt for the rebuild, you shouldn't have to do a setup on the rear end if you just install a rebuild. Just yank the differential out and install the kit, then reinstall the differential with the same shims in the same places. It's a good time to inspect your bearings, ring, and pinion as well. I think a Haynes manual might have the procedure for removing and replacing the differential, though I'm not sure.
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Tom