If everything is fine. Id work on software, areodynamics gearing to increase fuel economy. thats only if you want to go to more agressive approch. try this site I have attached a link on it.

 

Idk if they do this in Mississippi but during winter in the northern states they put additive in both gas and diesel fuel so that it doesn't gel or freeze as easly, and it doesn't work well for combustion. So pour mpgs. Also with it being winter people idle their vehicles longer to warm it up and obviously if your standing still while the engine is running your not getting anything for mpgs. Just a thought.

 

turned it down to stock , getting 19 now

 

Excellent!