Cummins turbo surging

My Volvo used to surge like you described under acceleration, and it ended up being the two ports in the venturi tube were blocked with carbon. On a Volvo, it's a pipe that sits between the EGR cooler outlet and the pipes where the exhaust gas and fresh intake air are mixed. There is also a sensor on the pipe that measures the difference in pressure between the two ports.

I'm not sure how similar the ISM is to the ISX, but I would probably go through the EGR system and clean it up. Here's a link to a thread that might help. The DPF stuff won't apply to your engine, but I would think a lot of the EGR components should.
Cummins ISX CM871 Technical discussion

If you do try to clean your EGR system, just make sure you can get parts like hoses and boots, in case you end up damaging them upon removal.