GMC Envoy XL Forum : “HOW CAN I GET BETTER GAS MPG OUT OF MY 2003 ENVOY XL”

They are not known for fuel mileage, but I would recommend that you dont "jack rabbit" for stops, drive the spped limit, keep it tuned and stay on top of all oil changes, you might want to look at a better exhaust and air intake, this will help make the engine more effient. the 5.3 get 13MPG city and 16MPG on the highway, you should see an average of about 14MPG mixed driving the 4.2 dosent get much better mileage. They are heavy trucks and they were not designed for fuel mileage.

here is a link for your fuel rating

http://www.fueleconomy.gov/feg/calculatorCompareSideBySide.jsp?column=1&id=19161