The cp3 is rated to 800hp while the cp4.2 is rated only to 535hp. The cp3 is the better pump.
Many duramax owners are swapping to the cp3.
2022 London Aire 4551 * 2022 GD Imagine 2800BH * 2021 RAM 3500 DRW * 2020 Wrangler
HAM: WD4LOW NHSO (Newmar Hoot, Sevierville Original)