well if this is your first diesel you gonna have to do so studying and tinkering and experimenting. another thing about engines are no two are alike. you may have 3 trucks exactly a like but all three perform different, handle different and shift different. small things you do on one that makes a noticeable difference may not even be noticed on the other. you also must remember 1mpg gain is not much nor is 1hp, but if you do multiple things that each gives you small gains, well as the old saying goes pennies make dollars. a good straight thru exhaust system to let it breath along with a good air intake system is a good place to start. some sort of lift pump to supply the common rail pump with an abundance of fuel, and I didn't mention but I hope you've already shut the EGR down. use the best quality 5-40 full synthetic motor you can get and for myself I also run a quart of full synthetic lucas oil treatment on every change. lucas is tried and proven, I use it in every part of every motorized thing I own from my garden tiller, lawn mower all way up to my big tractors. in my cummins truck I can actually document a 1-2 mpg difference fuel mileage just from using the fuel injector treatment and another 1-2 mpg difference when I add the oil treatment. now probably the biggest difference will be a good tune from green diesel or someone very familiar with this engine setup. another experience I had was better fuel mileage on hot tune rather than eco tune, but I don't have a problem keeping my foot out of it most of the time
. now if you plan on keeping it a while I would get a good convertor and shift kit for the tranny, if not youll regret it later. if you lift it, add mud tires and keep it full of junk that's gonna bring your mileage down. now, don't just listen to what I or any other one person says because theres so many variables that relate to fuel mileage, what altitude you drive, flat or hill, hot or cold, city or highway, single passenger or 5 ppl, weather conditions, driving habits, speed, towing, the list just goes on. but your very lucky to have found this site because theres some very knowledgeable courteous helpful ppl on here that have so much information posted you can spend weeks going through all of it. and personally I would try to read trough all of it over time because if you keep this thing long enough youll probably run across the same problems as everyone else at some point.good luck and go enjoy you libby