19.9MPG isn't abnormal.

Do this. Fill your gas tank all the way (until the pump clicks) and reset your trip meter. Then drive it until the gas light turns on and fill it up the same way again. Take note how many miles you drove and divide that by how many gallons you just pumped (example : 325 miles divided by 13.832 gallons = 23.496MPG) and that will tell you your mpg.

Its best to fill up the second time at the same pump you did the first time.