I tried applying a boolean modifier so I could make some holes inside a mesh, but the result was horrible shading. I've tried smooth lighting and an edge split modifier with sharp edges, but still nothing so far. I even added a new knife cut near the ends so it wouldn't be as noticeable. It's really bugging me, please help! Split concave edges just made a bunch of triangles with even worse shading.
Try selecting your entire mesh in edit mode and hit [ctrl + n] to recalculate normals. This should fix the shading..