[zyNoT]

Could be injectors, timing and fueling actuators, turbo sticking, EGR sticking (if emissions still on), engine running in the wrong mode at the wrong time, etc etc.

CM870's are notorious for injectors going bad and timing and fueling actuators wearing out. Since they have an air-driven turbo actuator, if you have a simple air leak in valve box or lines it can cause turbo to stick in the wrong positions.