Do you ever get a TSC or check engine light after the drop? If the drops are very short (say under a second), you may not. But if they are longer, you probably will. This would also be a sign of speed sensor failure.
I have the exact symptoms, I tried cleaning the grey plug right above the tranny below the air box but I had no luck, am I checking the correct place? If I am is this the speed sensor aswell? Ive gotten to many speeding tickets and when I say "Ossifer i was only going 0" isnt working anymore.......lol