One of the issues I had with my Glock 20C when it was new was that the factory installed the wrong spring loaded bearing for the loaded chamber indicator (LCI) extractor. The pistol worked fine for about 200 rounds, but then started to fail to feed and eject. I replaced the extractor with the older non-LCI version and the correct spring loaded bearing, and that solved all issues. Might be worth looking at after you try going back to the factory barrel.  Here's a link that shows the difference between the two. The front of the LCI bearing is longer than the older version.

http://www.lonewolfdist.com/Products.aspx?CAT=175