If you are running 15" wide tires, then I'd suggest just skipping anything else and buying a Detroit Locker. They are about a bulletproof as they can get. I'm attaching the Eaton main differential page address.
http://www.eaton.com/Eaton/ProductsServices/Vehicle/Differentials/index.htmThe drop-in lockers have one major disadvantage and that is they can only have two pinion gears. That also goes for the mini-spool. A purpose-built limited slip can have four pinion gears, like the Power Lock, or it can have a completely different design.
I also like the E-locker as 90% of the time an open diff drives better. Then you just lock the differential when you need to. The Mercedes-Benz Gelandewagen has the option of three lockable differential units, one in the front axle, one in the rear axle, and one in the driveshaft. I had a drive in one in a desert setting and when all three diffs were locked it'd just go in a straight line no matter how the steering wheel was doing. Open the center diff and turning was possible, but difficult. With only the rear diff locked it steered almost like an open diff, just some extra effort going around corners.
There is a plethora of limited slip or locker types on the market. Call DoctorDiff.
R.
