I have an 03 TL and it just started doing something weird. No CEL. I'll be driving on the highway around 70mph or so and if I give it gas to where it needs to down shift, not even WOT it will randomly shift I'm guessing into 2nd or 3rd. It down shifts so far that the tires have actually chirped a couple times. It feels like I slammed on the brakes when it happens. I have noticed it at lower speeds too driving through town but more on the highway at higher speeds. Anyone ever experience this and what was the fix? I'm hoping it's not the transmission or torque converter.

 

Have you tried hooking up a reader to see if you have any codes that didn't throw a CEL? Possibly a bad speed sensor, I had one go out on my Dodge and the tranny did all sorts of weird stuff.