I don't know if you can get 20-22 mpg, but I can give you few suggestions that may improve your fuel economy a little bit. Here is the link to the EPA report on your fuel economy.
http://www.fueleconomy.gov/feg/noframes/11439.shtml
Depending on the climate where you live, you can use 5w-30 oil instead of the standard 10w-30. In fact Chevy started recommending this in the mid nineties in order to meet federal fuel economy guidelines.
Drive like there are eggs under your pedals...both gas and brake. Gently press the pedal, slow steady increases in speed and slow down early for your stops.
Slow down 5 mph (you will be surprised how much this helps).
Pick a route with the fewest starts/ stops. Don't go 15 extra miles to stay on the freeway, but if you can take a road that has stop lights instead of stop signs, there is a good chace you will not find every stop light red, but stop signs always require stops.
I am sure that you are familiar with most of these, but if you pay attention to these details, you will probably see a 1-2 mpg increase.