It might be helpful if you posted where in the world you are located. Because there is a pretty darned good knowledge base on this forum and you might get directed to a gunsmith in your area that really knows his stuff. It would also be really really helpful to post what model you are having problems with.

BTW, my suspicion would be either an improperly fitted DA sear or a Hand/Extractor Pawl interference issue. However, if you have an N frame such as the 629 or a High End 686 Performance Center model your issue could be as simple as a trigger stop pin that was installed backwards. Point is different models can have minor internal variations and without knowing what model you have it's difficult to help you sort things out completely.

Finally, as it's a new firearm under warranty I don't think you should fool with it a bit. As you have seen the turnaround on warranty repairs is pretty quick. I think that you should contact S&W again and send it in again. Yeah, it's a PITA. However, keep in mind that shipping a firearm is an expensive thing to do and every trip back to the warranty center costs S&W something in excess of 80 dollars. Somewhere around trip number 6 back to the warranty center it gets to the point where it would have been cheaper for S&W to replace your revolver instead of trying to fix it. Point that out to Customer Service and perhaps they will tell the Repair Dept. to get it right this time.