Doug,
+1 to what Hippo stated.
Also, I followed your post on Tony's site (sbmar.com), and advise you give him all of the info and photos he requests. He is very knowledgeable and experienced with Cummins, and will most likely be able to provide good suggestions on how to go about determining what is going on with your engine. He is a no nonsense kind of guy with years of field experience, and is not a "paper smart", but is a "real world" smart kind of guy.
Ensure that whoever does further investigation into your engine, either follows Tony's suggestions (copied from his post):
"Did the “tech” perform the most obvious tests based on the symptoms??
Put a 0-100 PSI analog gauge on the
on-engine last chance fuel filter to “see” if you were having fuel supply issues? I believe pressures there are in the 80-90 PSI range when running on a 6.7
Did he 100% assure the that the one-way fuel check valve next to the electric fuel pump down by the ECM was not installed backwards– We have now seen two of these with symptoms very similar to yours. Pics of this on this web site.
https://www.sbmar.com/articles/qsb-6-7-fuel-hook-ups-and-fuel-direction/
Did he put a analog vacuum gauge between the engine and the fuel tank and monitor it while running?
Did he cut open the on-engine fuel filter and dump it into a clean glass container to “see” what is getting to it ( past your off-engine primany filters system?
ECM alarms / codes are great but do not always pin-point issues like you are describing ?"
or have the Tech explain the reasons why (in layman's terms so you can fully understand and/or relay to Tony) that test is not needed or useful.
Scott at Helmsman should be able to apply pressure on Cummins to get this issue resolved quickly, and it is in both his and Cummins best interest to do so.
Good Luck.