I was having trouble with low shots as well. I had no problem with my revolvers and could even fire a better group with my old PPK. Like you I finally determined it was my trigger control. Installing the next larger grip size (medium) helped a lot. I also changed my hold slightly so that my finger wasn't wrapping around the trigger. That brought the POI up to where it should be. Since then my shooting with my MP has improved a lot. I can now pretty consistantly hold 3" groups, center target, at 25 yards and 2" at 50ft. I have the M&P 40fs but do most of my target and practice shooting with my 9mm barrel.