[JLA]

sounds like a recoil spring issue. Did you install a recoil buffer? Or change the recoil spring?

Reason i say is I came across some fancy square wire recoil spring in my parts box and intalled it in one of my 1911s just to see. And it did exactly what you describe. It wouldnt allow the slide to travel rear far enough to lock after the last shot.

Another possible cause, and it is also recoil guide and spring related.. does it have a Full length guide rod? IF so there is a possibility the recoil spring is in backwards and binding on the guide. Some 1911 recoil springs have a coil curved in to grab the recoil guide so when you undo the bushing the spring and plug dont fly away. if you have one of these recoil springs on backwards on an FL guide it will bind like that. I had a guy bring me his TRP that was locked up becasue the recoil spring cut a groove into the guide and somehow got stuck. I got it apart. smoothed the burr and turned the spring back around and it worked perfectly.