Very hard to diagnose problems like this without having the gun in hand. Someone said it's like doing surgery over the phone.
Perhaps you have a trusted, experienced gunsmith in your area? If not, I would suggest contacting S&W Customer Service....either by e-mail or by phone. email:
[email protected] TX: 1-800-331-0852.
I'd be happy to look at it for you, but the government frowns on sending firearms through the mail.