1994 311 Excavator SN 9LJ00380 stalling

I am having stalling trouble with a 1994 311 Excavator SN 9LJ00380. It blows black smoke and stalls, or nearly stalls, when putting a load on the machine, or when the cylinders for the boom, stick, or bucket are bottomed out. Also when turning machine. All filters have been changed and I verified machine was not in "limp mode" at the switch. Anyone have any ideas how to diagnose and repair this problem? I have read a few other post with some other machines having the same trouble, but not a 311 Excavator, so, I don't think they will pertain to this excavator. Please help! Thanks in advance for any help...

1994 311 Excavator SN 9LJ00380 stalling