Maybe, guys, but . . . I don't know of any instance where a gasoline engine performed markedly worse with higher octance fuel . . .
The heat energy of "regular" fuel may be greater on a miniscule level, but . . . doubt the difference detectable even on a seat-of-the-pants meter.
Fuel contamination, as suggested, seems a more likely culprit to me.
I'd suggest draining the fuel bowl, and draining a few ounces from the fuel tank also, THROUGH THE RESERVE PETCOCK POSITION. Why RESERVE? That's the lowest outlet in the tank; and--condensate settles near the bottom.
Some alcohol-based fuel treatment, like Heet, wouldn't hurt anything.
Blaming loss of power on higher-octane fuel condemns and innocent characteristic, IMHO.