As they always say, check the cheapest problems first. If it's your grip, it costs you nothing to change it. If not, you might need a new magazine and see if that cures the problem. Besides, that way you get an extra magazine anyways so that's not a bad problem to have.
I used to have an S&W99 in .45 ACP that had this sort of problem as well and I shoot with low thumbs so it was either the mags causing the problem or the pistol itself. Fortunately that pistol was such a dog in the accuracy, handling and controls department that it was just easier to sell it than buy more mags for that thing.