[Fatty]

Has anyone of legitimate credibility verified that the toyota ECU actually alters the tune to suit the gasoline (octane rating)?

If so, it'd be the first I've ever heard of doing so. That'd be a pretty advanced ECU. The only way the engine could do so would be to advance the timing up to and just to the edge of engine knock.

Running higher octane fuel would in theory result in more power if like stated before, the ECU could run more advanced timing and/or lean out the fuel a little more to make more power.

I highly doubt that the ECU has this capability. Again, without a wideband input, the only way it COULD do so is to advance the timing such that it was just at the point of activating the knock sensor.....and I highly doubt that Toyota would do such a thing as it would be only a matter of time before you had a bad fuel/air/spark exchange and had damage to internals.

In some engines, namely high compression, high performance types, running higher octane fuel actually yields more power because the engine runs smoother. (with no change to the tune).

But for the most part, running higher octane fuel is nothing more than added insurance against engine knock...especially in hot Summer months where towing uphill in 100*F heat would DEFINITELY benefit from running 93+ octane.

I can tell you that the amount of any increase in fuel mileage you experience will NOT be equal to the cost increase of the premium fuel.