From all I have determined, you are correct. It comes with something called ALSD, Automatic Limited Slip Differential. I asked the sales guy about it and he said it was the same as a locking differential, but from all of my research it is not. Probably one of the biggest hits against the Tundra. I have found a company that can install a true locking differential in a Tundra.
Which begs the questions, "Why would Toyota not do that from the start?" My opinion is what I mentioned prior; most off-road testing and design is based on rock and sand, not snow and ice. I suspect the ALSD works great in sand. Most the truck review sites claim it works good, but none of them tested it on a snow-drifted frozen 12% Wyoming slope with 1,500# of people and gear. That is when you need a locking differential. Or when you break through a iced-over creek like happened last week and you find yourself in ice, water, and mud up to the door panels. You want all of it pulling you out of there, not whatever the computer thinks you need. Most of us are experienced enough to know more of what we need and when we need it than the computer that is probably programmed by some dude who thinks off-road demand is driving your truck from the parking lot down to the surf to pick up your board.
I made that mistake once. I was in a hurry to buy a new Titan before year-end, for tax purposes. They told me they could trick it out the same as the Pro4X package, except for the locking differential. Big mistake. It cost us a day of hunting in Nevada. Thanks to NVLongbow, the day was rescued. If I had a locking rear differential, I could have backed out of this hole. Rather, the rear end was sitting on decent tracking, but without the locking rear differential, it did not have the ability to pull the front end out of this spring that looked like a small mud hole from the driver's seat.
I don't have a "before" pic, but here is a "in the thick of it" pic. Good thing photos do not have audio, or this would be adult-rated.
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Here it is, with all kinds of brush and rocks under the jack so we could lift and fill underneath. It would sink into the soup as soon as we dropped the jack, even with filling debris under the tires.
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Here is the "after" pic. Finally, we cobbled together enough straps, wire, and rope that NVLongbow could pull me out with his little 4-banger Jeep. Note the foreground where you see rocks sunk into the mud. Not sure how many yards of softball sized rocks we hauled to find a bottom to that hole, but it was a lot.
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Needless to say, that was the last season for that Titan without the locking rear differential. It had 56K miles on it when I traded it and it was running great. I still see it cruising the street of Bozeman, six years later. But, I vowed to never again be caught without a locking rear differential on a truck.
It is that issue that is going to be a challenge for me to get comfortable with buying a Tundra; is the Tundra's ALSD as good as a locking differential in times like that?