I hesitate to comment at all , as I am an ancient slow swimmer myself but it sounds to me as though you have the ability to go faster but are probably not pacing your races correctly. I would guess that you are going out too fast and inevitably slowing at the end. I could be wrong of course. How do you normally split a 100?
I take it you are swimming SCY?
Terry has written about how he coached the sprinters at West Point, which may prove useful to you.