Fuel system work - RPM Drop

[Porterave]

Engine DD15, 2 Filters fuel system, Odometer: 714 273 miles, Engine hours: 17115, No deletes

After working on the fuel system the truck has an rpm drop after 1min to 1min 30sec on a cold start. A cold start, meaning truck is parked for more then 2h to 4h. Also this only happens on high idle, for example when I set it to high idle to build up air quicker on cold starts. If I turn the engine on and leave it as is on low idle, it won't drop rpm's.

No fault codes related. When driving no issues. No cranking issues truck starts right away. Only happens once on a cold start cycle.

I am attaching the Diagnostic Link Software graphs of the rpm drop and corresponding rail pressure drop, desired rail pressure and low pressure side readings.

Work done on fuel system, at first:
-Water separator filter
-Primary and Secondary filter
-Leaking Injector fuel lines 5 and 6 replaced
-2 Rail feeding lines replaced (As per manual when replacing injector fuel line 6)
-Banjo bolt washers and banjo bolt (As per manual when replacing injector fuel line 6)
-Reprimed system using manual prime pump only, started right away no issues.

Work done troubleshooting rpm drop on high idle:
-Replaced water separator dome, vent cap, collar
-Replaced primary filter cap
-PLV (pressure limiting valve) open counter found >50 (95) and replaced, didn't solve the issue
-Replaced again O-rings of 2 filter caps and O-rings of water separator dome and vent cap.
-Replaced again the 2 filters and water separator filter
-Re-torqued rail feeding lines and injector fuel feeding lines (not replaced)
-Fuel system integrity test with Diagnostic Link software is successful, no leaks detected
-Rail pressure bleed down when engine off is in specs, 1 min +- to bleed down to 9 bars default.
-Low pressure values in specs, minor drop when rpm dip - it is found on the graphs.
-Repriming with the hand pump on a cold start didn't prevent the rpm dip.


I am focusing on what I disturbed when working on my fuel lines and filters, hoping that I didn't inadvertently damage anything else. It first seemed to me an air ingest on the low pressure side, not sure now. I'm wondering if this is a low pressure side or high pressure side issue?
Can the injector fuel lines or rail feeding lines cause this issue, should I replace them again?
I still didn't replace the high pressure side filter cap, should I?

Any suggestion would be welcome.

Thanks for all of this.