The Duramax diesel engine family has shaped GM’s heavy-duty trucks for nearly 25 years. Born from a joint venture between General Motors and Isuzu, the Duramax replaced the aging 6.5L diesel and launched GM into true competition with Cummins and Power Stroke.
Each Duramax generation is defined by its Regular Production Option (RPO) code — LB7, LLY, LBZ, LMM, LML, and L5P — and each represents a major shift in power, reliability, emissions technology, or design philosophy.
Below is a complete, diesel-enthusiast-focused look at every Duramax generation:
its strengths, weaknesses, key updates, and why certain years are still sought after today.

