^x2. In addition, you likely would not know if it is tuned or not. Hopefully it is not. Check the exhaust also to make sure it is OEM and not catless or otherwise "missing" parts. it is very likely the plugs have been regapped to smaller than stock gap, which would make the engine run rich. Pull them, measure the gap, check condition. If you don't have a raw fuel smell, we can probably eliminate injectors. F150 guys like to "roll coal" where you see plumes of black smoke when accelerating ...
Any performance issues other than the black smoke?