There are several issues with E10 fuel (10% ethanol). First, it is a bit unfriendly to some polymers in the vehicle's fuel system, though only 10% of ethanol does not do much more than speed up normal deterioration. Second, being an oxygenate E10 effectively makes carburetor vehicles run a bit leaner (modern vehicles with oxygen sensors are not affected in this way: the engine management system just injects more fuel to compensate). Third, you use a few percent more fuel: E10 requires more fuel to provide the same amount of fuel energy, and it requires a richer air/fuel ratio. Fourth, ethanol has a higher octane level than 91 octane normal fuel, so unless the oil company changes the mix to compensate for this, you might end up with a fuel that is a fraction of one octane number higher than the conventional fuel. That is a slight advantage if the vehicle is prone to detonation.
I do not know of a reason why a 1996 Hilux would run better on E10. I am guessing that the model is new enough to have fuel injection and an oxygen sensor, so it shouldn't make any difference to the way the vehicle runs, except for a barely measurable difference in the fuel's octane level.
Premium fuel has a different mix of ingredients: a higher proportion of high octane components and a lower proportion of low octane ones. Since your vehicle only required 91 octane fuel, I don't see why it would run noticeably differently on 95 octane unless the fuel company was careless and allowed the Reid Vapour Pressure to rise compared with the normal level suited to the time of year. My guess is that for one reason or another, you either had contaminated fuel, or unseasonable fuel (if the gas station's supply of premium unleaded was old stock from the winter, and they sold it to you in summer, you might have had hot fuel handling problems due to excessive vaporisation of fuel in the fuel lines).
