In the June 2000 issue of Four Wheeler magazine they tested a Nisson Xterra. Over 8,285 miles, this small SUV produced an average of 16.52 mpg. In the July 2000 issue of Four Wheeler magazine, they tested a 2000 GMC Yukon XL 2500, equipped with the new 6.0L gas V-8. A diesel engine is the best powerplant for a large vehicle, and this explains why. Fuel mileage of vehicles equipped with a 6.2 or 6.5 diesel engine can vary quite a bit depending on vehicle health, transmission options, gearing and driving habits.
Speed is more critical on a diesel than a gas engine.
On the highway, in the 50-75 mph range, the fuel economy will go down about 3 mpg for each 10 mph increase in speed. This condition is perhaps the most significant factor in obtaining good fuel ecomomy. Fuel economy may vary as much as 5 mpg in a given vehicle with different drivers. Diesel engines have about half the useable rpm range as compared to a gas engine. A gasoline engine will produce acceptable fuel economy over a fairly wide rpm range.