Cummins m11 excess smoke, intermittent miss

early 90s cummins m11 in a International
We keep having an intermittent miss... or at least that's what I would call it, it will run fine then as you are rolling down the road it will begin to pop and sputter like its timing is out.. no smoke during. These spells will last usually 30-60 seconds, then afterwards the truck will pour black smoke on take off like its either over fueled or is starving for air.

Running a high ratio of ATF seems to make the miss go away, or make it less frequent.

I'm leaning twords the injection pump, however could a faulty ecm cause this?
why does it seem like this motor is over fueled? It will only pour smoke during certain times..

Scratching my head with this one, appreciate any insight... in my short time ive only ever worked on mechanical Cummins like the L10 and Big cams.


Thanks.