01 N14 injector/wiring issues

Hello,
Have a 2001 Sterling 9500 dump truck with the N14 non red top. The truck has always had a miss since we got it. The ecm has been replaced a couple times and injectos have been replaced once. The miss got significantly worse to the point it seemed like an injector was completely out. I used this video to figure out where the problem was originating from. Figured out it was the cylinder closest to the cab #6? Replaced that injector and all the wiring harness and pass thru connectors on the rest. Ran the best it’s ever since I had it. About 200 miles later it’s completely missing again. Same process in the video and it’s #6 again. Noid light flashes as it should so it would seem the ecm is good. What’s taking out this injector??