cummins isx injector

[Hammerhead]

Did you do a leak test before you pulled the injector?
If yes, were there any bubbles?

Sounds to me like, yes you got a bad one.
Have you tried moving it to another cylinder to confirm the symptom follows the injector?
You may want to try that to completely eliminate the possibility of some other issue. Moving the injector to follow symptoms is part of the troubleshooting tree, and they may ask if you did that before warranting it. Less than likely though as if it was another issue, it should be the front bank, not just one cylinder.