First of all, welcome to superdutydiesel!! This is a great website with a wealth of information.
A turbo-back 4 inch exhaust would be the next best thing. you will really notice a difference in throttle response should gain some mpg.
In my own opinion, the superchip really isnt the best tuner out there for mileage. I had one and experienced a lot of flaring when shifting from 3rd to 4th gear. When money allows, get a custom burned chip from dp tuner or something of the like. Someone else will chime in with more info on the chip, but an exhaust will definately get to pointed in the right direction