Need help diagnosing a problem with a ISX15

This engine has been having this problem for well over a year now. It's an ISX15 CM871 with roughly 665,000 miles. It will plug oil filters every 5,000 to 7,000 miles. It originally started the day that the turbo and EGR valve were replaced under warranty around 450,000ish miles. At first it was plugging filters around 15,000 miles, but slow started to get worse. The engine oil would be caked with soot, but multiple oil analysis showed the oil contamination and wear metals to be fine. at 663,000 the truck done it again with only 5,000 on a fresh oil change. I got fed up with not getting any support from a local dealer so I went into an in depth diagnosis (I am a mechanic for the trucking company that owns this truck). I always use Insite and Quickserve for my work. So im troubleshooting this engine and going through my steps with no coolant, fuel or blow by contamination, and everything else in the steps are fine. I get to the step of checking injection timing and stopped there, because we do not have all of the specialty tools for in depth work of that kind. After i dropped the oil filter out and changed it earlier and let it drain, I cut it open and laided the pleats out and found metal flakes. Put a magnet to it and found it to be iron. Dropped the oil pan and checked the rods and mains. All the journals look great and the bearing look normal for that many miles. Pulled the valve cover and found a bad cam lob on # 3 intake and rocker. 2 weeks later the engine was back going. I replaced the cam, cam bearings, oil cooler, oil pump and shimmed correctly, the faulty rocker arm, rod and main bearing and thrust shims, set the engine base timing to factory specs, set the gear train backlash to factory specs (I always do my work by the book or at the least try, especially when it comes to progressive damage work). Truck has been running great. Better then it has in quite some time. They had a local driver running the truck for about two weeks before sending it OTR. After 2000 miles of trouble free performance the truck dropped oil pressure...... FOUND A STOPPED UP OIL FILTER!!!!!! 2000 miles with crystal clean engine oil and no performance issues and the filter stopped up again. I am just at a lose of words for the truck. Oil brand and filter brand are not the issue either. This engine has had DELO 400LE, Rotella both CJ-4 and are cummins approved, Fleetgaurd LF9080 factory oil filters and Donaldson P559000 oil filters, engine uses ULSD fuel, and probably 1 to 2 gallons of oil between services at 25,000 miles and ALWAYS plugs the oil filter. IF anyone familiar with this problem can help shed some light about this, I would greatly appreciate it. Thanks.