OK, now its the new years so I'll post again :-)

Lets talk All-Wheel Drive (AWD) vs 4-Wheel Drive (4WD), and the influence of limited slip differentials (LSD).

From what I understand, AWD vehicles will get stuck when just one wheel loses traction ... UNLESS they have LSD somewhere in there (front axle, rear axle, and/or front-to-back). I think they'll typically have a LSD front-to-back, which provides a minimum of two drive wheels.

4WD vehicles typically have no front-to-back differential, which is why they "buck" when doing a tight turn on a dry surface. This means that for them to get stuck they need to lose traction with one of the front AND one of the rear wheels ... UNLESS they have LSD somewhere.

My 4WD Chevy Suburban with the option code G80 has a limited slip differential in the rear axle. When the two rear wheels spin at a differential rate (difference) more than 100 RPM (1.7 rotations per second) the rear axle will lock up side-to-side. This provides drive from a minimum of 3 wheels.

So I need to get the rear wheel spinning at a fair rate to lock the rear axle - and keep it locked long enough to get me going. I still need some time in 2WD on an icy parking lot to get a feel for that. I wish my truck has a way to manually engage the rear differential lock, so the rear wheels would be locked BEFORE the wheels start slipping.

BTW, my John Deere 3320 tractor with mechanical four-wheel drive (MFWD) works in a similar way to my 4WD Suburban. In MFWD mode the there is full differential on the front axle and the rear axle, front-to-back is locked together, and it has a manually engaged rear axle differential lock. So can provide three drive wheels.