Both the 6.6l and 3.0l diesels use a Denso fuel system. GM went to the Denso system after all the problems with the Bosch CP4 high pressure injection pump failures on the 6.6l. There have not been many issues with the Denso fuel system on either Duramax. They stopped using the Bosch fuel system in 2016 (L5P in 2017 was the 1st gen 6.6l to use the Denso fuel system).
The 6.6's were the LB7's and it was the injectors, and the 2011 to 2017's with the CP4's. The LLY, LBZ, LMM, and LML saw very few failures from injectors or pumps. My son's LBZ, I bought it new, handed it down to him, 350k and still running the original injectors and pump. LBZ's were last non-DPF, non-DEF 6.6's built, and are sought after due to their reliability. Those 6.6's used the Bosch HPCR, which was a CP3 gear driven pressure pump. In 2011 the LML Duramax was introduced, which used the CP4 fuel system, and a new piezo solenoid injector, both were prone to issues.
The L5P has a Denso HP4 pump, which can't produce the rail pressures the CP4 and CP3 did, the injectors were changed from a Bosch Piezo (Used from 2011 to 2016), to a solenoid type produced by Denso to accomodate the lower fuel rail pressure of the HP4 pump.