Because my truck was smoking when I arrived in altitude, I was told to have my injectors rebuilt.  Having your injectors in tip top shape is particularly important, especially if your engine is direct injected.  Direct injected (or TDi as they're called) engines do not have "swirl chambers" unlike a 2H or 3B Toyota Diesel and must rely solely on the condition of the injectors to produce adequate "swirl."

Swirl is also the effect of pre chambers on indirect injected engines.  In order for diesel fuel to combust completely, each injector must produce adequate "swirl" which is a wide, fine mist pattern of the fuel when it is injected.  Otherwise, the fuel will not combust completely and your engine produces black smoke and has a loss of power.  Unburned fuel also increases EGTs which can cause damage to your injectors, piston rings, and if the EGTs are excessive, can create cracking in your engine pistons and head.