It is the 5.3 V8 not the V6. As for the 4WD it is 4WD not all wheel drive like most GMC's I have seen which means that in 2WD the front axle is disconnected and not turning the front differential like my 99 suburban did. Even at that the difference in city fuel economy between my 4WD and a 2WD suburban was only 2 to 3 mpg even turning the front differential constantly. So the net result of the 4WD is only that it is carrying the extra 300 to 400 pounds of equipment around, transfer case front diff and driveshaft etc. which is like throwing a small load of dirt in the bed and driving around. I would not expect a small payload in the bed of the truck to dramatically reduce fuel economy. That would be like putting two or three friends in your car and having the gas mileage drop dramatically, just not going to happen. The advertised mileage on the truck is 14 city and 18 highway. The factory ratings are determined with a professional driver generally downhill with a tail wind, or so it would seem. interestingly enough this truck exceeds the factory ratings on the highway but falls 5 to 6 mpg short around town which is why I would like to hear from someone with a similar truck and get some real mileage figures.