2006 5.9 barely runs
 

I have a 2006 Ram 2500 with the 5.9 cummins. It recently sat for a week and when I came home, i started it up and it ran really rough, like it was only running on half of the cylinders. It got progressively worse over about 5 minutes of run time and now it will barely start and when it does it blows a lot of smoke and won't hardly pull itself. It has 116,000 miles on it, is completely stock and has never been modified in any way.
About a year ago, when it was still under warranty, it did this same thing and the dealer replaced one fuel injector and the injector harness. I pulled the valve cover today and checked all six injectors and the harnesses from the injectors back to where it plugs into the connector at the valve cover gasket. All six injectors and harnesses have less than one ohm of resistance. Several years ago, the dealer replaced the ECM because the truck lost power when i was on my way home from work one night.
How can I check to see if the problem is the ECM? Also, is there anything else that could cause a problem like this? Any help is appreciated.

Wow those are weird problems to hit your truck! Try the wiggle test when running on the injector plug ins and the ecm main harness. Also make sure your battery terminals are clean and tight. Next would be CP3 test. unplug the FCA on the back of the CP3 it will max the fuel pressure to the injectors. Should rattle like a bad diesel! Plug it back in it should smooth out in less than 30 seconds!

We will test the injectors for flow and return flow for $10 each. YOu can get a good estimate if you have a good scan tool.

To be perfectly honest, sounds like someone filled your truck with gas not diesel.

I have seen this caused by an open in the pass through harness/valve cover. Also a shorted injector can do this. With the valve cover removed ohm check all your injectors. Before you that drain some fuel from your fuel filter into a clean clear container and check fuel quality.