This is pretty close to what we are experiencing. We never saw the weird symbols on the dash display like we did when the original trs went bad. If the car is put into "D" it acts up and won't shift... it seems to stay in 3rd gear no matter what we do. If it is put into "3" then the trans shifts up and down automatically as long as the trans isn't shifted manually into "D", we haven't tried shifting it manually on the highway yet. Also, the check engine light has been on ever since the trans started acting up a few weeks ago.That is exactly what my '05 does, also. It is not necessarily the TRS, so you should get it scanned first. When it's the TRS, the dash gear indicator will show some weird symbol instead of the gear you're in.
I have to drive mine in 3rd around town so it does not act up. If I have to do any freeway driving, I first let it get up to speed (around 55-60 mph), let off the gas pedal, shift into Drive, watch the RPMs until they go low -indicating it has in fact shifted into drive- and accelerate slowly thereafter.
If the engine light comes on, yes, it will be stuck in 3rd gear, so just pull over and clear the code with a scanner and turn the ignition off and on 3 times to reset.
This may not be the same issue your car has, so get it scanned (or buy a cheap OBD2 code scanner/eraser and sca it yourself) if the engine light comes on.
My problem is most likely caused by a damaged "brake C clutch piston seal" in the transmission, which I have not sourced yet, as I simply do not have the funds to do so.
Good luck with yours!
I'm waiting for my wife to borrow a code reader from a friend so I can see which codes are still showing. It showed 700 and another code (don't remember which one).
I am going to clear the codes and reset the computer by trying the instructions seen on this thread in a later post. If that doesn't work, I'll try adjusting the TRS and clear and reset again...