If you have a Silverado or any other GM product with a 5.3 from like 2007 to 2011 you probably have the problem of pretty crappy mileage and burning oil. I've had this truck since it had 40,000 and now I'm at 125K. Burn at least a quart every 1500 miles and my mileage has gone from almost 17 to 15 and change. Anyway I've tuned it up, ran some seafoam through the vacuum system and a couple other fuel/decarb things over the years and it would get better but just for a little while.
Buddy told me about a little thing to disable the AFM (doesn't let it go into 4 cylinder mode). Bought it and have been using it for about 1000 miles. Oil has just barely gone down and mileage is at 16.3...range technologies AFM disabler. Was $189 and seems to be doing what they say it will. Just wanted to pass this along. Love the truck, hate the motor.