I'm going to cheat here because I got carried away elsewhere... I'm a miser, a hypermiler who has ridden far enough on a bicycle to sympathize with the machinery that moves me, and when I first got a '90 f250 7.3 IDI I was seeing 22-24 mpg depending on how much highway driving and how many hills. It (The White Buffalo) was 2wd 4spd auto, srw, reg cab, power nothing, with a/c, and it would idle along happily whether loaded or empty, at about 1300-1800 rpm for me, getting its worst mileage empty on twisty mountain hairpins in norcal, 13-15mpg (a/c running). That poor truck had been run down as a (family) construction company truck until the tweaker (son) I bought it from inherited it from the company and bumped a bimmer with it, but the engine chugged dependably along despite nothing else on the whole truck showing any sign of ever having been maintained, repaired, or replaced. It moved me and everything my wife and I owned, from CA to WI, and I averaged 23 mpg at ~55mph indicated, ~50 actual, right in the steep part of its torque curve, and the slow end of the slow lane. In WI it moved supersacks of grain, 2-5k# at a time, around the hills and farms of the SW corner of the state, getting 17-19mpg until I found its replacement. It wasn't good at starting below freezing, and 2wd made getting firewood off my hill take extra time, and then I got stuck after unloading at one snowed-in farm... So I found Pullet, a frankentruck '90 7.3 idi f250 reg cab 4wd zf5 srw with a cushion bumper sitting on 35s (since removed) with a straightpipe out the side and a gooseneck hitch. A/c deleted, cruise control steering wheel and fancy radio added. It's been getting about 14mpg, except when I was getting firewood in LR4wd, when it got 4.5mpg.. but I was hitching to bigger and bigger chunks of trees and still upshifting. I've got some questions for y'all about its quirks, but it just came to New York weighing and pulling many tons and getting 10-12mpg. Speed was not impressive, but the (massive) job got done and everybody lived.. and now I'm tempted by a turbo all over again.. Engine is stock, but it smokes grey on startup and black if I floor it towards redline, but that's rare, I'm cheap and usually not in any hurry. Seems like a tiny turbo could help me keep speed and be less of an obstacle to others whilst also getting me nicer mileage, just has to kick in at low revs or I'll (almost) never get use from it. Anyway, (TL/DR: ) I've got approximately no experience working on diesels or trucks, but I'm patient and interested. I've owned two '90 7.3s, and I want this one to last forever and keep doing everything I ask of it.