I received my replacement UIC upper yesterday.  The machining and finish are much better than the original one that I received months ago, however I am having a few new problems with it.

I am also using an AX556 lower like the OP and the new UIC upper does not fit my lower properly.  
The first UIC that ADM sent me fit it fine but this one has a gap at the back above the rear takedown pin and it doesn't seat properly on the lower.  
I had to press down on it with all of my force and tap the rear takedown pin in with a hammer to get it on.  Even then you could see this gap.  I think maybe the coating on the back of the upper is too thick or something.  Not sure, I will try to get some pictures to better illustrate what I mean later.  I had to use a punch and hammer to remove the rear takedown pin to unmount it.  I am using a V7 rear takedown pin and have used these pins on other builds so I know they are gtg and that it is not the problem.

The other strange problem I encountered with the replacement UIC upper is that I can not remove the port door rod.
I can usually pull these out with my fingers, but I tried using a pair of pliers and then some vice grips and the damn thing still would not budge.  I'm now thinking that it might be glued in or something.  I am going to try to tap it with a hammer a few times to break it loose and then yank on it again some more.  I can't imagine that the rod is threaded in but I will try "unscrewing" it as well tonight and see what happens.  If all else fails I will break out the Dremel.

Mine has the same issue with the port door. Not sure how they are in there.

My port door rod pulled off with needle nose pliers and a bit of force. Went back on with help from a small hammer and punch.

Pliers and vice grips couldn't hold it well enough so I took a pair of side cutters and made some deep enough grooves in the rod and then held them in place while a buddy hit them with a hammer.  We eventually got it out and I had to pound in the new rod with a hammer and a tap once I got the new door installed.

I also used a drill bit to open up the rear takedown pin hole.  I can now fit get the rear takedown pin through it but I still have to tap the pin out with a hammer to remove it.  Not ideal, but probably as good as I am going to get it for now.