* The sticker on the driver's side doorjamb: This sticker usually lists the axle ratio. Look for something like "Axle Ratio: 3.55" or "3.73".
* The owner's manual: This should specify the axle ratio for your particular vehicle configuration.
* The build sheet (if you have it): This document details all the options and specifications of your truck.
* The vehicle identification number (VIN): A Ford dealer or online VIN decoder service can use the VIN to access the original build specifications, including the axle ratio.
Without one of these resources, it's impossible to tell you the gear ratio.