Hey Ferm, or anyone that knows diesels

[THEFERMANATOR]

From what I've read the torque app can be hit or miss. As to the sooted pipe, that is pretty well par for the course for a 7.3L. That is a DIRTY friggen diesel engine, and will haze even when in good condition. An exhaust leak at the turbo won't hurt your milage, if anything it would help it by lowering boost. When you're not running loaded, the less boost you run, the better the milage(more boost than needed is just wasted HP). It's sounding like you have either bad injectors, or a failing HPOP. Those engines normally get pretty good milage even stock, and the common causes of poor milage is injectors, or low high pressure oil pressure not allowing the injectors to properly atomize the fuel. Valve cover gaskets can also cause all kinds of problems like low voltage to the injectors, and not allowing them to run correctly. Theres a reason guys that work on those engines make BIG money, they always need work.