94 6.5l runs but jumps up and down when throttle is applied

[94 6.5l]

I have a 94 6.5 that was running great until the other day. Tried to drive home and when I started the truck it started fine but as soon as I put it in gear it went low idle. So put it back in park and gave it gas and it idled up but as I am holding my foot on the throttle it starts surging up and down. I was trying to idle around 1000 rpms but it jumps up and back down and pours out black smoke. It is undrivable as of right now. I am leaning towards it being a fuel issue but not sure what. Do you think it could be injectors have failed or possibly pump? Not real sure what to do from here hopefully y'all can shed some light on the situation

[Yukon6.2]

Swap out your PMD as the first step

[JohnC]

But before you do that, change the fuel filter and make sure you have a good flow of clean fuel to the injection pump.

[phantom309]

If it just " suddenly started" doing it,. Change pmd 1st,.
Fuel filters sneak up on you,. They don't just jump out and be "bad"