In Our Tests, We Found That Diesel HD Trucks Consume Significantly Less Fuel Than Gasoline Vehicles.
Although heavy-duty trucks are exempt from EPA mileage reporting, real-world highway fuel economy tests show that diesels consume much less fuel. Diesel trucks averaged 18 mpg, while gas-powered models averaged 15 mpg. This means a 20% improvement in fuel economy for compression ignition pickups. Still, of the 22 HD pickups we’ve used… Source: Car and Driver