Definitely check your filter, it sounds like you are over fueling. Are the 'throttles' split? Do you need more power to sync the engines? Could be the turbo, but go for the easiest first. Is your transmission/ running gear happy? No barnacles, cutlass bearing good, transmission oil recent?
Has it had all its regular maintenance? Oil and filter, coolant checked for condition and new filter, valves set, fuel filters changed?
Have you ever had the injectors checked and cleaned?
Is it possible that you picked up something in your wheel?
Do you have the Cummins manual? It also has some troubleshooting procedures.
I would do all the required regular maintenance first; if it has been done and none of the other things mentioned are at fault, then I would get a mechanic in, but not til you have done all the work first as it is expensive to pay out for what you can do.
"...Tongue tied and twisted, just an earthbound misfit..."