there are many more factors that go into loss of power and mpg after the fact of larger tires, and lift. the wider the tire, the more the power loss. and the larger the diameter tire, the more your gearin and speedo will change, and also results in some power loss.
Going down the highway with those big tires, and a lift, will greatly add to your size and weight, thus making aerodynamics about obsolete.
gear swaps, and power upgrades will net you close to stock performance, if not higher. but you will still have to have enough to overcome the weight. but being a diesel, power upgrades are crazy, so there are not as many troubles as there are for a gasoline powered engine.
