I was getting close to 20 mpg on highway completely stock. After adding high flow exhaust, K&N intake, and Superchips programmer and running it on the Fuel saver mode i can hardly get 16 anymore. In town and highway it is averaging terrible mileage (11 and 16), anybody have any reasons why this could be?

 

what kind of exhaust did you install for example i got 3 inch duals put on my 08 hemi and its dropped extremely because of loss of back pressure it haslittle to none and u have to have bp or else your gonna get low numbers like your getting... thats what im assuming is your problem

 

So with the minimal backpressure I get the horsepower advantage but lose mileage? I just replaced the stock muffler with a magnaflow high flow muffler and cut out that resignator muffler that is at the end.

 

More air = more fuel. Your superchip programmer adds fuel during different points within your fuel curve. If you add air without fuel then you run the risk of burning a hole in your piston. These trucks are manufactured to exact specs that allow them to produce good power and keep decent mileage.