Thank you RKG....after the "fix" last year it never acted up again. The pistol was returned to the factory five years ago. I had another issue with it and I did open it up---I could never get that spring in the trigger in the right position...what a goofy set-up. Looks like they designed it to baffle us. IMHO these things should be designed to be relatively easy for an average guy to be able to service them. S & W fixed it up and then I started have the problems mention. I never tried to adjust the main spring tension for a lighter trigger, but when it was mis-firing (as mentioned before) I did tighten the strain screw.
The strain screw should always be, and have been, tightened all the way in. Some shooters wrongly loosen the strain screw to obtain a lighter double-action pull. But one of the problems with that is, the screw is then likely to become looser via recoil, to the point where misfires occur. Swap-out the mainspring for a lighter one if you must, but the strain screw should always be tight in the frame.