oil change
air filter
fuel filter

do you have bigger tires?
I have a Supercharged 5.4 that see 100% 0-35 mph driving. I drive her hard from light to light and I still pull off 12.5 mpg every single tank...might occasionally dip into the 12 mpg zone on the harder tanks

 

I had a 2002 Silverado Ext cab with the 5.3 that got fairly good mileage, 16 to 17 around town and a little over 19 on the highway. When I bought my 2005 Screw, 5.4, 3.55 gears, 4x2, I expected worse mileage and was pleasantly surprised to find them almost identical. However, lots has happened since the truck was new that eats away at the mpg. The ethanol blend and much larger tires and wheels being the main culprits. The tuner didn't really give me any mpg gains, but, on the other hand, it is a lot peppier, more fun to drive and I do not drive it for efficiency, and still get the same mpg as the stock tune.