Hi, I hope someone can help with this question. I have a new 09 Silverado Ext. Cab. Lt with a 5.3 2wheel drive and 7000 mi. on it now.I took a 900mi. trip and I was only averageing 13.7mi per gal in the Hwy at 75 to 80 mph with an empty truck.The truck has the active fuel management in it that is supposed to help to do better mileage.This truck is suppose to do around 20mi per gal on the hwy and I was averageing 360mi on a 26gal tank. Could there be something wrong ? Or is the truck motor not broken in yet.

 

Your motor is broken in, the mileage will very greatly depending on the gear ratio you have and they are also calculated at 55 or 60 mph for highway.