Can you describe the FTE more specifically?
You said the problem became less with new extractor and spring.
The extractor holds the casing to the bolt face as the bolt travels rearward the bolt carrier presses down the rear of the ejector which cantilevers the front up into the channel on the underside of the bolt and should throw the brass clear.
The ejector consists of the ejector, spring and a pin/pivot that holds it in place.
A better description of the FTE You are experiencing would help guide advice on what to look at and what for. But the next item to check out would the the ejector and spring, I believe Oicani has a sale thread on ejector springs at the moment as well as 94 recoil springs but I do not know is a full size 94 spring would fit in a 5k setup.