In that case, perhaps you've gone from too loose to loose. The analogy I've heard is to hold it like a baby bird; firm enough that it doesn't get away, but loose enough that you don't crush it. If your loose grip had you on the verge of dropping the cue, it may have been causing you to unconsciously tighten up during your stroke just to hold on to the cue, and the effect would have been more pronounced on harder (faster) shots. The reason that you see so many recommendations for a loose grip is that a lot of new players grip the cue like it's a baseball bat, especially when they are nervous. In any case, I'm glad to hear that you found something that works for you.