Send it back to Kimber. Don't sink another dim in ammo, mags, or gunsmiths until they've at least taken it back in.
If you choose to disregard my advice on the matter, you may want to replace the extractor with an Aftec extractor, they reportedly make a 9mm 1911 run a little better.
If the problem is that the empty case is staying in the chamber, it's an extraction problem, not an ejection problem so start with looking at the extractor, Wilson Combat just put an article up on their blog for looking at extractor issues, stand by the for link.
Here's the article with video: http://blog.wilsoncombat.com/uncateg...-on-your-1911/