[69gmcc10]

I think you are a little optimistic on achieving a 5 mpg increase. Having owned several of these trucks a 3 mpg is ambitious but more realistic, and to get those last 2 mpg you will need to do some real fancy dancing on that gas pedal!

When I hear people talking about MPG I have a difficult time determining what they are trying to accomplish because there are several different mindsets that hunt the same animal. First, are they trying to minimize environmental impact by increasing economy. Second, Are they trying to save money by pouring less fuel it into the tank. Third, are they looking for bragging rights with there friends and don't care about the financial impact. Fourth, are they obsessed with efficiency and want to squeeze as much as possible out with or without a budget. Most people fall into one of these categories and sometimes several categories, what category do you place yourself in?

The real simple and affordable answer to this question is, keep the stock air box it draws COLD air from the fender and not warm under hood air like most aftermarket intakes. Also, the stock intake is designed to flow enough air for the 8.1 and is in no way a restriction, just buy a DRY high flow stock replacement air filter like AFE makes. 5.3L flow enough air to justify a 3" cat back exhaust system at wide open throttle, but it wont effect your economy much because that is all done at a significantly lower flowing 2000 rpm so just a free flowing 2.5" magnaflow style replacement muffler would be cheaper and be just as likely to potentially increase mpg. Spend money on a reputable tuner, hand held tuners only change change a few generic tables on your trucks computer, a computer flashed tune will consider many variables, tighten up the tolerances of the sensors on your truck, and also increase the drivability for about the same price or less of a hand held hypertech style controller.

Maintenance work will be your next best and cheapest secret for economy. Make sure to keep the MAF sensor clean and service everything accordingly.

I have an 01 1500 2wd with a 5.3 with an afe air filter. It only gets driven in town and I beat the piss out of it so mpg is not good, about 14.

I had a 03 1500 xcab 5.3 z71 Spectre CAI, no cats, stock tune and it got about 17.5 on the highway and 15 in town.

I have a 03 1500HD, 4wd, 4 door, 6.0, 4l80e, stock in town 11.5 mpg and highway 14. Spectre CAI, 4" exhaust, had electric fans (took off, no improvement on economy), custom tune from Black Bear performance and in town now I get 12.5 mpg and on the highway I get 16, 17 if drive under 70.

You can spend allot of money chasing better economy and you would be better off just converting that money into fuel and pouring it in the tank (Dollars Per Mile). But, if you want more Smiles Per Gallon there are allot of things you can spend your money on and you will probably enjoy every cent!