I have been doing my share of internet researching and besides fuel filter change and lift pump most other people make changes without a lot of evidentiary support. It seems people throw CP3's and injectors without really knowing if they are bad. I did some research on a professional mechanic database that accesses GM's info and it seems that they have a return rate test for the injectors that can at least assure an owner if the injectors are bad before spending 4K replacing them. The test for the CP3 were less precise more of a process of elimination but again I would try that before spending the 2K unless I just wanted to upgrade my components. They also had a test for the FPR on the CP3 but don't know how often they fail and the had a bottle test for the pressure relief valve on the fuel rail (forgot the name).

Since I now have a LBZ with the P0087 code I will do some more research and try to be systematic in replacing and hopefully from the cheaper side up instead of the other way around. One thing I can understand is the collapse hoses, fuel under vacuum (creating air bubbles) can both be cured by lift pump much less CP3 longevity which I believe the other manufacturers use in their diesels. I am surprised GM eliminated that component in their design esp since the previous design (6.5L) had lift pumps too.