2014 GMC Sierra Double Cab Puzzle

[[email protected]]

I currently own a 2014 GMC Sierra with the 5.3 Engine. I currently have 93,000 miles. In the last six months , my gas mileage has been very bad. I changed the wires and replaced the original plugs with AC Delco plugs. I have had the transmission fluid change as well as the Diff fluid changed also. However, the mileage continues to be bad. I can sit at a light and see the mileage indicator go down. Today I got up to 16 mpg. However when I started again the mpg is 14 mpg. Any ideas would be helpful. I drive mostly using the cruise control. 

[mafd2]

You posted this in the wrong section. This is for '19/'20 troubleshooting. Repost in the '14-'18 section.