CM2350 derate 6255 only no fault codes

[greg1227]

We have a customers truck 2018 Cummins CM2350 ISX 15 in the shop has been having derate messages popping up . Plug in Insite and see inactive 1659 fault 1 count . Clear code comes back on a day or two later . Was able to get him to leave the truck for a while and tried for hours to get code to come on . Finally yesterday did 2 injector performance tests and 30 seconds after 2nd test ( passed ) the 1659 fault is on and active 1 count . Display reads derate in 30 minutes . Truck is running perfectly no skips at all . Truck goes into derate , still 1659 fault active and 6255 inactive still 1 count on 1659 . Cleared all codes only active 1659 clears and 6255 goes active . Shut truck down for the night come in today and start truck , 6255 was now inactive cleared the fault . Did performance test for injectors and revs up and then drops back to idle and 6255 fault inactive comes on. So far we have checked resistance in harness from ecm to valve cover , from valve cover to injectors. We swapped number 6 injector to 4 , we swapped the engine brake rocker with 5 ( theses steps were done a week ago between his runs and 1659 continued to come up ) Now can do injector cut out test, no issues, forced regen , air handling test all with no issue as soon as injector performance starts 1 second kicks out and inactive 6255 derate code is up . Thought i read somewhere on CM2250 some had similar issues and they changed the ecm . I was told this ECM injector drive controls multiple injectors and may not be the issue because it only happens to cyl 6 and only 1 count any help would be appreciated