Automatic Transmission Problem

[nnanda]

I have a Corolla model NZE121 G package with Automatic Transmission Year 2001. This is an imported second hand car from Japan.
The problem I am experiencing for the past few days are as follows:
1. While driving (over 80 km/h) the RPM climb from 2 to 3 or 4 thousands suddenly.
2. The speed drops from 80 to 30 km/h.
3. When accelerating the the engine does not gear up.
4. Sometimes it last over a long period of time (10 mins) ; sometimes it last over only a few seconds (10 secs).
5. I'm getting this problem more frequently these days.
6. My mechanic has not been able to remedy the situation.
7. This problem has started since I drove in a water pothole on the road. It was raining heavily on that day. I don't know if the problem is because of humidity.
Would you please help me in sorting out this problem.
Thanking you in advance

[kenchi]

check your air filter maybe its wet of something... have you change your wheel from rigth to left? maybe there some problem with the electronics, check your ecu or ect ecu if your car have it, or maybe it could be the cut of velocity, there is something bad done in the elektronics, or the gear box could be defficent too or bad sincronized with the ecu

[fredk]

tranny trouble guy, its loosing pressure somewhere

[Toysrme]

On a lot of Toyota transmissions there is a kick-down cable that links to the throttle plate.
IDK if your car has one, but 9/10 if the transmission is acting funny with no previous signs the cable has fallen "out of adjustment". It sounds like it's too loose. Put it back in the center.

Check the tranny fluid also just to make sure everything is OK.

[Smokey4AGE]

Not sure, but is it possible that the transmision fluid filter got worked? maybe do a complete flush n replace filter...
my rolla is auto, but a 92, its prolly wrong, but i had the same problem when my oil was low... very low... my bad. ahahha

jus an idea...