[mmorello82]

My car did the exact same thing!! Small world! About a week or so after mine started doing it, it started shifting REALLY hard. Took it to the dealership and it turned out being the "pressure control solinoid". There is a o-ring around it and it goes back and leaks off pressure. When it does, your rpm's will "surge" because the torque converter is locking and unlocking. You can replace it, but it is located in the clutch packs, have to tear the whole thing apart. I just bought a reman, and no trouble since. This is what the GM dealership told me and I trust them, like I said no problems since. If you want, I can put up a exploded view showing where it is.