If the cylinder is locking up just before the hammer releases in double action it is good. Wouldn't take much more and trigger would bind before it released the hammer. The difference enough and to much is slight. I would check for end shake before doing any action work. How much does the cylinder move forward and back? If there is a significant amount as the gun is cocked the cylinder moves forward and farther from the hand so it can slide by the ratchet tooth quicker. A cylinder shim or 2 may be all it needs. If the the cylinder stop is engaging the cylinder and preventing it from turning it is fine. Some small amount of movement while in lock up is also acceptable. As the bullet leaves the chamber throat and enters the forcing cone it brings the chamber into perfect alignment. If there is excess movement it comes from peening in the cylinder stop notches (usually the far side, not the lead in side, as it stops the cylinder rotation). This can be peened back into place. It could also be slop of the cylinder stop in its frame slot.

But, don't go putting parts in it until it has been checked by someone who really works on S&W revolvers. Your post gives no information on your experience with them. Your thought of just replacing the extractor tells me you haven't got much as extractors very seldom work on cylinders they were not made with. Until the recent pinless design change the extractor and cylinder were match drilled as a set during assembly. The holes in one extractor star very seldom line up right on a different cylinder. Even a tiny bit of difference and it hangs up. I have had zero luck at it and I have a drawer full of various cylinders. There is a couple work around, but it isn't that easy. Someone with a small lathe and the right knurling attachment can redo the knurling the tip of your rod, BTW

More important is how does it shoot?