Ok quick question for you 5th gen guru's. It appears that the limited has a center locking diff, while the SR5 has a rear locker. So does the limited always stay in 4wd? Or is it like an 4wd on the fly type set-up? Just curious as to how the gas mileage is the same between a supposedly all time 4wd system in the Limited vs. the SR5 which is on demand. Both are stating 17/21.

SR5 doesn't have a locker.

Curious eh?
The LE is running skinnier tires and lower front fascias. The center diff is pretty efficient too. Read the link in my signature line for an explanation.

So skinner tires, and a lower fascia will offset the full time 4wd's gas consumption? Is that right?

Pretty much. Remember around town they would get about the same mpg regardless as the lion's share of energy required is to accelerate the vehicle and they weigh about the same. Turning that extra driveshaft accounts for a bit but it's easier to turn it slower than faster if that helps.
On the highway it's a little different as now the horsepower you need to maintain speed is to overcome the rolling resistance (tires) and force the brick through the air. You lose a bit (let's say 1mpg) turning that driveshaft but gain that back through less rolling resistance and improved (remember "improved" is relative here) aerodynamics. In reality it's probably close enough to be a rounding error up to the next whole number but believe it or not the skinnier tires help out a bunch to improve efficiency and the front air dam helps a bit too. Why do you think the Fords, Chevys and Dodge trucks have grille openings that close and low front spoilers?

1engineer, that is exactly what I was looking for. Thank you sir. If there is anything I can ever help you with let me know. I am a certified hvac tech, and also help my wife run a used car dealership ( I have access to carfax's, new/used car pricing, and all sorts of tools at my disposal ). I also have direct access to new Toyotas, Chevy, Gmc, and Buick.

Also, the 2wd models will get better MPG than any 4wd model because there is no front diff or transfer case to turn.

Even on sr5 and trails, the front axle on the drivers side is always spinning the differential planetary gears. This is slightly more rolling resistance than just wheel bearings. Also the transfer case itself introduces a slight efficiency loss as there is simply more mass for the motor to spin (even when in 2H).

With all else being equal (same tires. ride height...) the limited will get slightly worse MPG than a part time system in 2H. A 2wd model will clearly get the best mpg, but they are still not that great.

Like mentioned before. They are bricks and the motor is not the most efficient design in production. Direct injection and a better transmission would help a bunch, but it is still a heavy brick.

And just to clarify. The sr5 has a part time locked center/transfer case. The limited has a center diff that can be locked. Neither has a rear or front locker, but they both have atrac (a brake activated system that attempts to keep both wheels on an axle spinning at the same speed in crawl conditions)

Thanks also wfo9. Great info.

Limited has full time 4WD and a center diff. SR5 has PT 4WD, others pretty much covered everything else.