590 Super L skipping at low rpm

engine is a 4T390 that cranks and low idles fine but skips/sputters between there and 2000rpm. Runs fine at and above 2000. Black smoke burst visible at cranking and when it is sputtering. Bought used and thought was just a fuel problem. I have drained/cleaned fuel tank, replaced both fuel filters 3 times, checked/cleaned fuel lines, added Sea Foam religiously, had injectors tested (all fine) and tightened everything for air leaks. Also (don't know if related) the hydraulics seem to really...

590 Super L skipping at low rpm

590 Super L skipping at low rpm