It appears that most M&P users have the issue with the slide lock lever being designed for only a lock and not a quick one thumb release.  I have read other blogs(on other sites) in which they claim by calling S&W they will provide an enhanced extended slide lock/release lever assembly for free.  When I called S&W they said they have never provided such an improved extended release.  Anyone out there know anything different on this subject, and yes I have polished, grinded and rebent the original one with only little improvement. The last solution is to weld about a 1/2 inch extension plate to the lever and solve this problem once and for all.

Well just an update if anyone has similar problem: previously had purchased a S&W factory replacement slide stop/release, I used this new one to bend the thumb tabs outward while keeping the height of the tabs level with the frame, i.e. first try caused the bend radius on the right side thumb tabs( I wanted to make it ambidextrous so I bent both thumb tabs out); to restrict upper movement of the release.  It takes quite a little fooling around with bending the tabs but got them even in alignment.  In addition filed and polished the left contact surface to taper the 90 degree contact edge;  finally woolah put the puppy back together; the trigger spring takes some wiggling, and problem solved.  Now takes only one thumb without excessive effort to operate the slide stop with one thumb; while still holding slide back securely;  note it looks a little weird with the thumb tabs sticking out but it works considerably better.  Maybe this helps others with this dilemma.

That is great you were able to mod the firearm to feed your needs better, I am all for that but I wouldn't call what you were experiencing a problem.  

It is a slide stop, not slide release the problem is that you and other operators of the firearm are trying to use it in a way it wasn't intended.  

Great pointers though for modifying an inexpensive disposable part to achieve those results.  Midway, Brownells and Speedshooters all carry that part.