it just all depends, adding a programmer will help some, its hard for me to believe that a v-8 diesel is getting 25 mpg i call
on that one.. but certain chips/boxes/prgrammers will help you out... most now will raise rail pressure a little bit... with that being said helps the fuel atomize better. which in return burns off more fuel instead of waisting it, helping out your fuel mileage... for increases the truck needs to breath, i would go with an aftermarket air intake, open up the exhaust and add a chip or programmer.. the more air in and the more air out, the better off she will breath and help out your fuel mileage....:thumbsup
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