The difference in the GM systems, AWD vs 4WD is mostly in the front axle. The AWD systems don't lock the front axle and power is distributed to the front by a viscous coupling. 4WD systems (manual and electric) provide an electric full locking front axle and power is transferred using a chain system in the transfer case. The 4WD systems with the "Auto" button have electronic transfer cases so that when "Auto" is selected, the front axle is locked and when F vs R slippage is detected the t-case splits power to the front axle.

The biggest drawback to the AWD systems is lack of locking front diff. The situation was worsened early on because vehicles were available without a rear locking diff. So if somebody cheaped out on the option list, they could be in a situation where wheels on opposite corners were spinning free.

For the family grocery getter driven in mild to medium conditions, the AWD will be the better platform for the control it provides and ease of use. I personally like the increased flexibility of the electronic 4WD offered in the "standard" class of SUVs like Tahoe, Yukon and Suburban.

2WD with shift on the fly 4WD is the best. There is hardly a need for AWD unless you own an Audi or comparable car that is built around it. 4WD on trucks means the t-case is locked and will send 50-50 front and rear no matter what. There are no full time locked axles on any truck(except the jeep rubicon and dodge powerwagon front and rear, some toyotas-4 runner etc ONLY REAR, and those are all selectable). All are glorified limited slips...some are better than others. No manf puts limited slips in the front axle either(harder to turn.) The auto 4wd system(AWD), as found in GM trucks, tries to decide when it needs to engage and you can feel it surge fwd when the back spins out. Just put it in 4wd hi and forget about the jerky computer controlled crap. Put it back into 2wd when you dont need it.

Denalis etc have only AWD...different t-case, and do work in a more seamless manner than the awd found in dual use 4hi-lo-awd-2wd as found in other trucks. But you dont have 4lo, and the t-case cannot lock 50-50 front rear. GM calls there limited slip the G90 locking axle, but it is not locking. Like i said above....no manf puts real lockers in their trucks except the rubicon, power wagon, and some japanese trucks...4 runner etc. Only the rubicon and p-wagon have the locker in the front, and ALL are selectable on/off.

In order to make a locker or a limited slip in the front axle easy to drive you need to have auto or manual disengage hubs, or a fully selectable unit like an ARB, or detroit e-z.

It totally depends on the truck.

In some cases you can get both. my navigator has awd, 4wd hi, and 4wd lo. No 2wd. In normal driving, only the rear wheels get power (and there's a limited slip back there). When the rear wheels spin, the computer detects it and locks up a clutch in the transfer case to send power forward. If the clutch is active for too long, it automatically engages 4x4... which is a dog ring in the transfer case tying the front and rear together just like a typical 4x4 transfer case. If I want low range, I put it in neutral, hold the brake, and engage 4 lo.

In my dad's envoy, he has all the same options plus 2wd. In 2wd, it just shuts off the clutch feature and leaves it in 2wd all the time.

In a lot of vehicles, all you get is AWD. This is not as desirable as an option with AWD, 4x4 and 4 Low.

I would personally rather have all the options, like my dad's envoy. AWD is nice for the snow, because you don't have to worry about turning it off if there's an area of dry pavement. 4x4 is nice for off road, low range is nice for the launch ramp, and 2wd is nice when you want to do a big smoky burnout.

Oh... and almost no production vehicles (save for those mentioned above with lockers) have any type of locking or limited slip front differential. Very few front wheel drive cars are available with a quaife limited slip / locking diff (not sure on the exact functionality of that unit) but almost no 4x4 or AWD vehicles have anything but an open front diff. If a manufacturer claims to have a feature of this type on their front axle, it is almost always a system where the ABS detects wheelspin and applies the brakes on one wheel, thus sending power to the other (like the caliber srt4).

Rears frequently get limited slip from the factory (or GM's crappy "gov-lock" POS, if that's still around) and often get a "locker" aftermarket, either manual (cable, electric, or air actuation) or automatic (sensing wheel spin and engaging a lock not based on a clutch). True "lockers" are kind of finicky on the street and are really more for off-road use.

As quoted from my 2001 Yukon XL owner's manual:
So GM's 4WD front axle will indeed LOCK via electronic device. The rear axle is GM's excuse of a "locking" diff, but it does work at low speeds and throttle input, like a slippery ramp. A true limited slip would be great; do they make one for the 14-bolt axle?

When they refer to locking your front axle they mean it gets 50% of the torque, no more, no less. The transfer case is an electric selectable version...not lever. You do not have any type of locking mechanism in your front differential. The only front lockers available on any production vehicle are those found in the jeep rubicon and dodge powerwagon. Both are very similar to a detoit e-z locker and selectable. The GM G90 rear axle feture is their limited slip option that comes standard on z71's etc. it is a clutch type limited slip....dont know why they call it a locker. Ive installed detroit lockers on my previous full size bronco(with warn manual hubs so i can turn) and big difference...almost like welding the spider gears.

Well tell ya' what, you define "locking" for me. I'm pretty sure I understand the difference between the transfer case splitting power to the front axle and "locking" the front axle. When 4WD is activated, it's pretty obvious when you turn that the front axle is locked.

As for the rear diff, GM's unit isn't a clutch type, at least not what I think of (like an Auburn) when I think clutch type diff. It's made by Eaton, and it's totally open unless you spin a wheel below 20mph. If you spin a wheel at slow speed, it spins weights inside the diff to "lock" both wheels. The axle will stay locked until you go over 20mph. The engagement is about the worst I've felt, and in my truck it's pretty easy to spin a wheel over the "disengage" speed before it ever engages.

I have a escape with auto awd, but you can lock it into 4wd when it is messy out. works amazing, the little suv is a beast in the snow with good tires. have a suburban that has 4wd, is amazing in the snow in 4wd, but if in 2wd is pretty crappy. the auto awd system works fantastic

I had a AWD Astro service van for awhile and in heavy snow I gotta admit it was pretty phenominal.......after a couple of minutes you didnt really even know it was on .......you just drove around normally with awesome traction.......
Although even up here theres only probably 5 or 6 days a year that you REALLY need it.......and the question was snow not launch ramps......