With respect to premium resulting in better driving and mpgs in these trucks, I'll just say that the power of suggestion is a very powerful thing to one's mind.

I've seen this discussion/debate time and time again on the automotive forums I've been a part of since the days of dial-up and America Online (AOL).

It really makes no sense for the truck to have better throttle response and less downshifting running premium. Octane is a fuel's resistance to burn. Thus, higher octane fuels are more resistant to burn which is why they are required in motors with really high cylinder pressures. The current gen 1-GR isn't that motor. Plus, the benefits of higher octane would be present under hard, high rpm driving, and not low rpms or initial throttle tip-in.

As for downshifting, that is all related to engine vacuum and load and not octane. The transmission ECU senses a change in engine vacuum and/or load (i.e., higher load) and will downshift accordingly. It has nothing to do with octane.

If someone wants to really put this to the test. Take your 4Runner to a shop with a Dynojet dyno. Do 3 runs with 91 for about $100. Then full up with 87 and run that for a week or so and re-dyno on the same dyno and similar ambient conditions. I would bet the HP and TQ numbers across all runs would all be within 1-2% of each other which is typical dyno run variability.

Lastly, the higher the altitude you are, the less octane the motor needs (low oxygen in the air). That's why in high elevation areas you routinely see 85 octane fuel at pumps. It's not because the stations are "cheap".