I just got my truck back from the shop and when I was driving home I noticed that when I first push the gas pedal, it blows out black smoke but when I get to third, fourth, and fifth gear it blows out black smoke then it turns into a grey/white smoke? I'm no mechanic but isn't that usually a bad sign? possibly bad injectors? any help would be appreciated.
99 Dodge 2500 5.9 24 valve

 

yes the grey white smoke is unburnt fuel. What were they doing at the shop?