Stupid question (probably) about automatic transmission

I have a 2WD, V6 Auto. The options are D, 4, 3, 2, L. I don't understand why there are so many and would love to know the purpose.

4 is hardly a difference from D. I've used 3 once or twice to keep up with a TRD Pro Tundra uphill. What is the purpose of any of them, why not high/low? How would a 2WD even get enough traction to use that torque from 2 or L if stuck or something?

Genuinely curious, not hating at all. I'd just like to know if I could be using my truck better or something.

 

A few reasons.
But the main ones are are engine power, engine braking, and some what to help save wear on the transmission.

Your engine produces most of its power above 3,000 rpm.
Unless you are pressing the gas pedal down far/fast your truck will shift gears BEFORE it gets to peak power. If you ever tow anything with a good bit of weight, you’ll understand this, as the truck will constantly shift back and forth between gears. You would be better off leaving it in the gear that is closer to peak power for the speed you are traveling. Plus, it saves wear on your transmission.

Next would be braking, you can drop down a gear and use the engine compression to help slow down.
You won’t notice it as much with a 2WD truck, like you would a 4WD with low range. But it’s still effective at “higher” speeds.

 

In addition to what ^^^ said it’s also good for when descending hills in snow. You can use lower gears to slow yourself down and are less likely to skid out vs using your brakes alone. Or if you’re worried about your brakes heating up while descending steep passes and such.

 

Also:

You're right, there is very little difference between D and 4....normally. If you're towing a trailer, I've heard you should stay in 4th to keep it from hunting so bad......but that said, I never have and it's been fine.


So short version, I have second hand advice on this...but I don't follow it myself. So take it for what it's worth

 

As jproffer said, don't use D for towing.

D allows the transmission to use overdrive to get better highway MPG, but the overdrive is typically not designed to work under stress.

If towing, or if merely hauling a lot in the bed, you will help transmission life by keeping it in 4.

 

I always generally viewed the numbers below D as mainly for engine braking on long, steep downhill grades with 4 also the correct choice/selection for trailer towing. Other than that perhaps for L, 2 and 3 to hold the transmission in those numbers when crawling along in 4L in a 4x4, especially on very steep, slippery descents to keep the speed under control.

 

This is how Toyota describes the gears in the owner’s manual:
D: Normal driving (shifting into overdrive possible)
4: Engine braking (shifting into overdrive not possible)
3, 2: Stronger engine braking
L: Maximum engine braking

The manual goes into more detail when/how to use these gears. Additional relevant info from my 07 manual:

Be careful not to over-rev the engine. Watch the tachometer to keep engine rpm from going into the red zone. The approximate maximum allowable speed for each position is given below for your reference:
PreRunner
“3” ....... 138 km/h (86 mph)
“2” ........ 95 km/h (59 mph)
“L” ........ 55 km/h (34 mph)

Four−wheel drive models
Front drive control switch knob at “H2” or “H4”—
“3” ....... 138 km/h (86 mph)
“2” ........ 95 km/h (59 mph)
“L” ........ 55 km/h (34 mph)

Front drive control switch knob at “L4”—
“3” ........ 54 km/h (33 mph)
“2” ........ 37 km/h (23 mph)
“L” ........ 21 km/h (13 mph)

If you don't have an owner’s manual, you can download a free copy from Toyota’s TIS website.

 

You have 5 speeds. 5th gear is overdrive. If you put it in "D" the transmission will start in 1, then shift all the way up to 5th gear as you accelerate.

If you place the shifter in "4" the transmission will downshift out of overdrive down to 4th gear if you are in motion. If not already in motion it will start at 1 and go no farther than 4th gear. It will not allow it to go into overdrive. If you are towing a trailer or loaded heavy always use "4". The engine is working too hard with a load in overdrive, and you risk overheating both the engine and transmission.

I also find it best to use "4" if I'm not going to be going over about 40-45 mph for a while. The transmission wants to shift to Overdrive. But at slower speeds it lugs the engine, robs you of power and actually hurts fuel mileage in overdrive. OD is best used at speeds over 50-55 mph.

Using "3", "2" and "1" are normally used when going down hills to let the transmission help slow down the truck and reduce the need to use the brakes. When I'm driving in mountains I move to "4" all the time going up. But when going down I'll use "3", or "2" a lot to keep the truck at a safe speed and save my brakes. On the road it would be rare to need to go all the way to 1st gear. But I use it a lot off road.

Think of it as a manual transmission without a clutch. You can select whatever gear is best for the situation.

 

While driving down the Sandia mountains in Albuquerque was the only time I've had to "shift" my truck between those numbers. There are straight sections where you can be in "2" and then once you hit a curve you can shift to "1" to make the turn safely; didn't want to use my brakes much because it was a.. 10min drive to the bottom?