From late '43 onward the game changes from one of hunting to one of survival whilst also hunting.
Your tactics need to be adapted, you must be far more conservative and your tonnage scores are going to be predictably smaller.
If you are patient and stealthy enough though you can still get away scot free with even heavily defened convoys and task forces. There are opportunities for those that can get into the right position, but you must also know when to avoid contact and not press the attack.
the fun part is leaning to know the difference.
