Diesel Problem

[83ChevyK10]

Need some help to figure out whats wrong with my truck. Once it warms up to operating temperature it will randomly bump and blow puffs of black smoke out of the exhaust. Also at random it will rev up to around 2000rpm and bump it way do back to idle dropping about 200rpm each time. If anyone has had this problem or could give me some advice it would be much appreciated.