2.5L, V6 auto. tank refill: 10 gallons

is this bad? on a good average run, i get 180 miles on a tank (half highway w/overdrive, neutral roll on downhill, slow acceleration). on a bad run, it averages 140 miles on a full tank.

this means 18 mpg/14 mpg

shouldnt it be having 200+? does anything need to be replaced?
153k miles