You can't get mileage and "black smoke" at the same time. As mentioned not many are real keen on the black smoke thing, it just brings a bad name to the diesel world. As for damaging the injectors not really true. About the only two things that damage injectors are bad fuel filtration and dirty oil. No one here will recommend a "superchimps tuner, so look at DPTuner, Power Hungry Performance or Elite Diesel. Those are the TOP three programmers for the 7.3l. As for your transmission the torque converter will suffer first. As for mileage you can get better mpg with a chip if you keep away from enjoying the increase in hp and torque, but mpg is mostly driving style.