* Engine size: The 1999 Suburban came with a few different engine options (e.g., 5.7L, 7.4L). Larger engines consume significantly more fuel.
* Transmission: Automatic transmissions generally have slightly lower fuel economy than manual transmissions (though manuals were rare in Suburbans of that era).
* Driving conditions: City driving will yield significantly lower MPG than highway driving. Terrain, weather, and driving style all play a role.
* Vehicle condition: Proper maintenance (tire inflation, tune-ups, etc.) greatly impacts fuel economy.
Therefore, there's no single answer. However, you can expect generally poor fuel economy for a vehicle of this size and age. Expect to see figures in the range of 10-14 MPG in combined city/highway driving, with potentially lower numbers in city driving for the larger engine options. The smaller engine might achieve slightly better fuel economy.
To get a more precise estimate, you should consult:
* The owner's manual: This will list the EPA estimated MPG for your specific engine and transmission.
* Online resources: Websites like Edmunds, Kelley Blue Book, or FuelEconomy.gov may provide user-reported fuel economy data for similar vehicles.
Keep in mind that these are estimates, and your actual mileage may vary.
