My grand daughter complained her Scion was quick to 70 MPH but took forever to get to 80. It was because the carpet was bunched up under the pedal, limiting travel.
If that's not your problem, I'd get it to a shop. Running out of power may be annoying, but could be a symptom of something serious that may end up failing on the highway.
2000 Four Winds Five Thousand 28A (1999 Chevy 3500), Master Tow Dolly, 2012 Scion xB TOAD