I had the same issue with my 40c so I sent it to Burwell for a trigger job. Burwell Gunsmithing- Your M&P specialist It's a very clean crisp trigger now but still hard to feel the trigger reset.
My next gun I pickup (M&P 45) I will get the Apex complete trigger upgrade kit, the "RAM" kit is the one that greatly improves the reset. Welcome to Apex Tactical Specialties, Inc. All the reviews on the Apex kit are great.