You didn't give us much to go on.
What year is it? Was there any change between the pinched o-ring and changing the APP? What was the code?
Could be a lot of things. First thing I'd do is check the fuel delivery to the injection pump. Then I'd put a scanner on it and see what the pump is (trying) to do when it's acting up.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510