Update..
Got my M4 back from Benelli after a little over two months (Dec 4th-Feb 14th) and finally got it to the range. I'm happy to report I ran 118 shells of 00 buck from a few brands, mostly Winchester, without a single failure.
According to the report from the tech they changed out the extractor and deepened the extractor cut in the barrel extension.
I wish I could say my trust in my M4 has been completely restored, but I think its going to take a few more range trips for that. I'm a pessimist, I know. More like 98% restored..;)
Thanks again to everyone for all the previous input.