My 2005 Ram 3500 4x4 quad cab gets about 20 highway, but around 12 towing my 28' trailer with my 4150# Charger (combined weight about 9,000#?)
The Smarty is supposed to be a really good programmer. I have an old Edge Juice. It plugs into the injector harness and does not change anything in the stock computer, and it has the monitor that displays different info like EGT.
Adding timing and a bit of power may help a bit, but don't expect too much mileage increase, maybe 1 MPG?, but the extra power is nice.