No valve body mod. Just checked my tranny fluid, which I only changed about 4000 miles ago, if that, and I could swear it smelled burnt.

Today, it did the chattering thing while shifting into 2nd as well. Sometimes it wraps like the rear end is going to fall off, other times, it just loses power and hesitates while trying to shift down. Sucks.

No codes being thrown. Like I said, the MIL came on and flashed during one of the bad shifts, but as of right now, no codes are stored in the ECU.

It sounds to me like the torque converter can't manage the power anymore and is causing this, but I really don't know what they do when they start failing.

If you say it's toast, then what do you know of as far as signs that a TC is taking a dive?