Update: Mechanic cleaned the valve body including the filter but the problem still persists. Tomorrow he will do an overhaul.

Same situation with you lantizx, the mechanic said that the ATF of my car has so many residues and he thinks they were from broken gaskets.

Based on his way of diagnosing the problem, I think he knows what he is doing ~ I really hope so heheheh :D

I'll try to document the mechanic's solutions:
- Clean transmission filter
- Clean valve body
- Replace ATF

Todo: Overhaul