Det/ problem

i had a detroit do the same--would cough only during the long hard pulls---never any other time---it had a variable turbo as well--an 06--i noticed when it was new you could really hear the turbo spooling up and down while sitting at a light--as the engine got more miles it seemed to quit doing that--and it was no screaming hell for miles/p/g just over 7 imp. and that was working to get it there---
but for coughiing at the initial start p--i would lean towards a turbo controller--not an injector or turbo itself

 

that same truck--turbo cut right out--went to 0 boost--took it too detroit in severe limp no power mode--they replaced a turbo controller and it was ok---it still coughed on the hills--but at least i had full boost the rest of the time

 

The hill coughs, same as I had on the Cummins, are caused by the variable vane turbos. I can see where the turbo controller can explain the issues, especially on startup/flats.

 

? here as i dont know but does that truck have the electronic throttle pedal.I have heard they can act like that.something you could check yourself with ohm meter.

 

could the egr be causing this prob?

 

Just throwing this out there.
When was the last time you checked your air intake for obstuctions and air filters for cleanliness. I sounds like its starving for air.