Many 04 and 05 duramax engines suffer blown head gaskets. It is mainly due to some defective turbo components and design. If you want to really understand it here are some links. It is worst when towing heavy in elevated areas on hot days. The hardware changes suggested here should be in every 04 and 05 duramax to help avoid what you experienced.
http://killerbeeperformance.com/induction/induction-overhaul/
http://killerbeeperformance.com/lly-overheating/lly-induction-overheating-explained/
http://killerbeeperformance.com/lly-overheating/thermal-feedback/thermal-feedback-primer/
http://killerbeeperformance.com/lly-overheating/thermal-feedback/thermal-feedback-loops-in-turbocharger-applications/
