fuel pressure dtc causing confusion

[dtdiesel]

I have an employees truck setting a p0191 in a 2011 lml. Upon discovery of code I recommended removing regulator for inspection per pip4949d of si. After inspecting metal debris was apparent. After discussing info it was decided that a cp3 conversion was the proper solution to his 200k cp4 failure. A replacement cp3 fleece conversion with an upgraded pump was performed. After installing a tune with fleece's flow vs current table applied and vehicle started all seemed to be well. Pressure matched desired and seemed to run great until we returned from test drive and truck set p0191 again at idle, the only time it has ever set it. I have deleted code for time being, but am curious to what exactly this code's importance is and what problem may or may not still be causing. I really hope we did not immediately wrongly accuse the pump for failure even though it seems highly likely given the metal debris found on the regulator screen, but seems that maybe previous tuning may be the cause or it's a separate problem with the tuning that has always been there, any insight to this issue would be greatly appreciated

[dtdiesel]

I would also like to note that to my knowledge dtc was not present prior to tuning, it wasn't an immediate result but a new one in the following weeks

[dtdiesel]

anyone seen this?

[anarchydiesel]

It is not uncommon to see that code with a CP3 swap.

[dtdiesel]

this code was present prior to swap, but I've been recently informed that the 2nd regulator is most likely cause, not a huge issue just demining that problem was apparently not in pump pressure at all.