Welcome to Just Answer Dodge my name isXXXXX realize that all my answers are based solely on the info you provide me....
This is a fairly common issue with these engines. It is being caused by excessive fuel return to the tank due to some bad injectors. The fuel system will need to be tested to isolate which injectors are causing this to happen and then those injectors will need to be replaced.
The testing requires a couple of special fittings so your Cummins or Dodge dealer will need to do these tests.
My customer does not like the dodge dealer I work on all their heavy trucks and they seem to think I should be able to fix this I'm an expert at heavy diesel engines but know very little about the 5.9 are these fittings expensive and how do they work
The fittings are about $30 a piece and you can order them from SPX Miller tools. These fittings simply allow you to measure the amount of fuel that is returning to the tank and if the combined return rate is excessive, then you use another fitting to isolate the specific return rate for each injector and this narrows down the faulty ones.
When these engines get to the point where they don't want to start, you can pretty much count on at least 3 injectors that are bad. Although expensive, many times it simply makes sense to replace them all because the other ones will likely fail in the near future.