I have a 2010 Chevy Silverado standard cab long box 4x4 with the 4.8L engine. I have a tonneau cover on this vehicle. The best mileage i ever got was 20 mpg hwy. I recently purchased a Fuel Genie and had it installed. I was very skeptical that this would do much of anything for my fuel economy. On a trip last week i tracked my mileage and to my surprise i was getting a whopping 27.0 mpg. MythBusters was full of bunk. I just now added a K+N cold air intake and filter to my truck as im shooting for 30+ mpg. I have only ever run regular unleaded fuel in this vehicle. I will be making a trip outa town in 4 days time so ill track my mileage once again, The numbers are as follows 542 kms and 56.59 litres. NOTE (converted to imperial gallons) not US gallons. 1 gallon = 4.54 litres. 1 mile = 1.06 kilometers. 542 kms = 336.78 miles and 56.59 litres = 12.44 imperal gallons. works out to 27.07 mpg. Wish me luck

 

2004 2500 6.0 crew cab 4x4 with the keys cranked running 33's. CAI and a ARE fiberglass cap getting 12.6 interstate and as low as 7.6 city....I could only dream of 19 mpg's.