Dark paint colors are the hardest to use, because of this problem. I have seen this effect where you wind up with a wall with slightly different colors and sheen's, especially when viewed close up. A few things could be happening.
1) You're applying the paint too thick per coat.
2) Using too thick of a roller cover.
3) Too much thinning of the paint or added an excessive amount of paint conditioner.
Thin coats of paint are better for dark colors. This will help with keeping the tint from pooling into blotches. Also using a thinner roller cover will help. I like 100% lamb's wool covers, but they can be floppy. Use 1/2 inch covers for smooth or lightly textured walls.
Thinning the paint can be crucial. A small splash of water or Floetrol (latex paint conditioner) will help the paint flow and even itself out on the wall, reducing the blotchiness. The opposite can also happen if paint is thinned too much. You will have to play around with this idea as every paint manufacture has slightly different products that benefit from different amount of conditioning or thinning.
Another thing that can help is ending each roller stroke in the same direction, typically down. This will make the roller pattern even and pointing in the same direction.