Fuel Average gauge stuck?

I just bought a 2017 Toyota Yaris iA, 35k miles on it, and it's
a manual. When we first bought the car driving around in
the city and on the highway the average would jump around
at random based on acceleration, speeds, uphill, downhill
etc. I filled it up one day with premium gas and now the
gauge stays pretty constant between 30-35 mpg. A good
example is on my way home from Work there is a large hill
on the highway and coming over and down the guage
would read 170mpg, now it only reads 35 mpg.  I did try
resetting the fuel economy meter but it's still doing the
same thing. Is there anything else I can try?