I'm not sure if this is a feature on Toyota cars alone, but I currently drive a '99 Avalon XLS and in addition to the D3 mode which I know disables overdrive, right above the radio near the top of the dash in the center panel, there's a button for "ECT Mode" which I've heard is a way for the car to increase the RPM threshold before shifting gears therefore making it more agile.
Occasionally I've used this feature when doing highway driving as it makes switching lanes much easier (since I don't have to floor the car) but I wanted to know if this feature is the same as disabling overdrive because I've noticed lower fuel economy when driving, and also when in standard stop and go driving, leaving the ECT on seems to be a safety hazard as the higher threshold doesn't mix well when accelerating from 0 to 30 or so.
On some forums people have said this feature is for towing or for driving up hills, but as I also have the overdrive kill switch, I'm wondering if this is more of a performance feature vs. for utility.