Duramax was designed as a "joint venture" between GM and Isuzu.
Reports indicate that Isuzu was primarily responsible for the engine's design, while GM's engineers were tasked with programming, calibrating, and integrated the engine's electronic systems in a manner suitable for their application.
All Duramax diesels are assembled at the DMAX plant in Moraine, Ohio. GM is currently the majority stakeholder in DMAX, whom reportedly bought out Isuzu in 2002. - DuramaxHub.com
Back in 1996 General Motors was finalizing plans for the next generation of full-size trucks, code named GMT800, and at that time, GM had only 3% market-share for the Diesel Powered HD pick-up truck segment. In order to have a winning truck, GM had to have a winning Diesel powertrain.
At the same time, a small group of stakeholders led by the Planning Group, reviewed proposals from all the possible Diesel engine manufactures for the all new truck.
The decision was reached to go with a proposal from one of GM’s partners – ISUZU Motors LTD, recognized worldwide as a leader in Diesel engines. The proposal had been developed as a part of a strategic 90-day study conducted by ISUZU and GM, relative to ISUZU’s role in the GM Global enterprise
See The Duramax Diesel 6600 Story from GMHeritageCenter.com to learn more.