https://www.merchant-automotive.com/LML_Duramax_CP3_Conversion_Kit.aspx The CP4 was introduced as a cost reduction to the LML platform since a smaller amount of fuel is required when running the more efficient injectors. Since its introduction it has proven to be less reliable than the CP3 used in previous Duramax platforms. NEW Bosch OEM CP3 No Tuning Required CP3 is already re-calibrated to match the LML stock CP4 fuel curve Kit is designed to replace the less reliable CP4 that comes stock on