Stalling with my 6.5
 

I have a 1994 Chevy Suburban K2500 with a 6.5L diesel, completely stock. Recently it has been blowing black smoke when you have to give it throttle, and the engine light comes on but goes right off when not giving it throttle anymore. Also it started stalling for no reason and seems like the fuel cuts off for a couple seconds while you are driving for a couple times. When the fuel cuts off, there is no throttle response until it comes back on. Everything I researched points to the PMD/FSD, and no, it wasn't relocated yet. Before I go replacing it, I want some other opinions. I don't want to just throw parts at it.
Thanks