* Check the vehicle's sticker: Look for a sticker on the driver's side doorjamb or in the glove compartment. This sticker often lists the axle ratio.
* Check the owner's manual: Your owner's manual should specify the axle ratio for your particular vehicle configuration.
* Look at the differential: This is the most definitive method, but requires getting under the vehicle. The ratio is stamped on a tag on the differential housing itself. You'll need to clean the tag to see the numbers clearly. It will typically be written as a fraction (e.g., 3.55:1 or 3.73:1 or 3.92:1).
Without knowing the specific trim level and engine of your 2001 Dodge Durango, I cannot provide the correct gear ratio.