The deal with limited slip is that when one wheel spins, it takes that power and applies it to the other wheel. And if you hit it from a dead stop and you're going straight, you should get equal power going to both wheels.
Many of the off roaders use air locking axles. They have a compressor that blows air into the differential and the axles lock up 100%. You don't ever want to run them on the street, as locking axles don't work well on pavement.
Now as far as 3/4 tons not doing well in the dirt. My PowerStroke diesel weighs 450 lbs. more on the front end than if it had a gas engine. It makes the rear end relatively light, which makes the rear wheels spin easier.
I've had to load a bunch of kids in my 2x4 pickup bed a couple of times to get it off a grassy hillside. But I figure I could pay for a wrecker to tow me 75 times and I'd be at a break even for the initial cost of 4wd in a 3/4 ton truck.
