Cm570 hesatation underload

[Red]

I seem to have air in the fuel return hose. I set up a test tank to eliminate sucking air from hose or truck tank and still have air. So this might be the course of my problem although id exspect the fault to be more consistent if this was the case and i have no hard start or shut down or ruff idle??. I have ordered a cummins tool/part to preform a injector leak by test as I have seen on Rawze you tube, exspensive in Australia but $500 for the tool. This I hope will let me determine if its sucking air at the IFSM system or injector.