Need to know were to start to get fuel econonoy with my 6.6 duramax?

Put a good cold air intake on such as one from Airaid, or AFE, and depending on the state you live in you can straight pipe it which will make it sound awesome and help your milage, and add a tuner I recommend an Edge Juice with Attitude and that will make a big difference as long as you don't run the chip to hot I would use stages 1-3 only that will give you much improved mileage but won't tear up your engine/tranny.