I have had my Cruze now for 15 months. Bought it used in almost perfect condition with 32000 miles. I now have 55+ thousand miles. And since I bought it, every time I fill it up, and check the numbers, the trip computer says X gallons used, which varies anywhere from almost a gallon to exactly a gallon LESS than what I put in.... any suggestions as to how to adjust this? Thank you. Darren.