Been Doing this for a year

[Inaris]

being that you revised your earlier response to correct the firs mistake you are mostly correct. As you are restating what I said, the 4/3 is in releation to the number of usable gears a vehile has. i.e. newer automatics offer up to 6 gears, whereas older models offered 3.
The fact is that when pulling a heavy load in an automatic, the tendancy is to shift down, in some cases even out of overdirve to help get the engine working harder so that the vehicle won't slow down. This is one of the drawbacks of the Automatic transmision. Newer trucks are handleing this better with more advanced monitoring equipment to recognise a need for an automatic downshift to compensate the uphill battle.
Yes, drive is limited to a certain amount of gears, ALL-1 where 1 is reserved for overdrive.
Now to be honest, I don't even think they include overdirve anymore as there really wasn't a point to it aside from one more notch on the gear box. Most New automatics just have them all listed, especially cars that use the Autostick type technology.

 

[ag3]

What are you talking about!? I didn't edit any of my posts.

 

[Inaris]

I'm not going to argue about this as I saw something different posted by you after I had posted my first reponse. Indicating about the oposite of what you have since stated. Could have been a glitch, but I know what I saw. Any way. My response was to the post. which due to me not quoting has been lost. No harm. Here is a bit of info for you both on the "proper" use of overdrive:

Generally speaking, overdrive (O/D) is the highest gear in the transmission. On most cars the automatic transmission has 3 speeds and Overdrive (forth speed). Overdrive allows the engine to have less rpm with higher speed in order to have better fuel efficiency. When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 30 - 40 mph depending on the load). When it's off, you limit transmission shifting by third speed.
In normal driving condition the overdrive should be always on.
You may need to switch it off if you drive in mountains area.
[The automatic transmission automatically shifts from OD to the 3-th gear when it feel more load. When it feels less load it shifts back to the O/D, but under certain conditions, e.g: driving uphill or towing a trailer, the transmission can not decide to stay in OD or to shift into 3-th speed and it starts to shift back and forth. That's the time you may switch it off and help the transmission to decide.] .
You also may need to switch it off when you want to slowdown using the engine braking, for example, driving downhill. [For more details, check your owner's manual]

 

[OCC Fan]

i asked my drivers ed teacher and he had a long john kerry reply in which he didn't answer my question but he said that overdrive helps by going more miles per gallon. other than that. i don't even know.

 

[beedubaya]

John Kerry....LOL!

 

[ag3]

Inaris - lol - I did not edit my post. Trust me. What you read is beyond me.