Common problems with Duramax diesel engines include air in the fuel lines, fuel starvation, water pump failure, overheating, injector failure and harness chafing. Some of these issues are preventable with certain modifications.
Air in the fuel lines and fuel starvation are often caused by the design of the fuel filter housing and the fact that the injector pump must suck fuel from the gas tank as it is not equipped with a lift pump. This is most problematic for the 2001 to 2004 LB7 model filter housings. Expect to replace the water pump after between 80,000 and 100,000 miles. This issue is consistent in all years and is simply a flaw in the factory water pump design.
Overheating is more common in the Duramax diesel, especially 2005 and older models, than other trucks, though not all are effected. It stems from fan clutch failure and possibly a dirty or clogged radiator. GM redesigned the fuel injectors and offered a seven year extended warranty after the 2001 to 2004 LB7 models consistently failed prematurely. The wiring harness experiences chafing and may cause the truck to ride rough, not start or lack power. The only remedy is to replace the faulty section of the harness.