* Engine: The 2013 Ford F-250 offered different diesel engine options (likely a 6.7L Power Stroke V8). The specific engine significantly impacts fuel economy.
* Configuration: Was it a regular cab, supercab, or crew cab? The weight of the truck varies considerably.
* Drivetrain: 4x2 or 4x4? Four-wheel drive reduces fuel efficiency.
* Towing/Hauling: The biggest impact on fuel economy. Towing a heavy load dramatically reduces MPG.
* Driving style: Aggressive driving reduces mileage.
* Terrain: Driving in mountainous areas reduces mileage.
To find a reasonable estimate, you'd need to specify the exact configuration of the truck. Then, you could look at EPA estimates from 2013 (which would be the best source) or various online resources that compile fuel economy data from owners (like fueleconomy.gov, though that site may have limited data this far back). Keep in mind that real-world mileage often varies from EPA estimates.
