I stopped believing in God years ago, but it has nothing to do with my stutter, I just genuinely believe that he doesn't exist. I'm really sorry to say this but I don't think it's a valid reason to stop believing in God because of your stutter, if you believe that there's a higher power that created the universe it doesn't make any sense to stop believing in it because it gave you stutter or it gave your grandma cancer. I'm not saying you're wrong or anything I'm just stating my opinion (an opinion that may be wrong), wish you the best.