[Powerstroker]

Hello All, Cool site I just found here. I was wondering if anyone can offer any tips for my truck. It is a 2000 Ford F350 Superduty, 7.3 powerstroke diesal, crew cab, long bed, dually, zf6 speed manual shift truck with 4.10 gears. It has 112k miles, in excellant condition, averaging 18mpg, 80% highway, 20% city, only sees 1000 pds in the bed with a camper top, occasionally pulls a 5k pound boat, but mostly daily driver. At the moment, mostly stock. I have replaced the stock air box with an s&b intake. I am installing a 4" exhaust, and a SCT tuner. I want to squeeze out every mpg humanly possible, and was told to change the rear gear to 3.31 or 3.55. Anyone have any thoughts on my plans, or anything else that would increase the mpg. I was told to get with Big Dave on this site, but don't know how to find him, he is supposed to be a diesal truck guru. Thanks all!