Got my 40c back from S&W. took it to the range yesterday and it has the same problem with sluggish slide movement. No improvement whatsoever. The paperwork said they did a "barrel modification" (couldn't see any evidence of a change), replaced the extractor and extractor spring. When I saw that report I was almost sure that they had not addressed the issue. I am no expert, but I know enough to know that what they did had no relevance to the issue. That tells me they were clueless or didn't care to take the time to solve the problem.

I have the same problem...actually now it is worse. The slide now locks back prematurely on the occasional shot. I made sure my thumb was nowhere near the slide lock lever. I guess they are hoping I will just go away.