Originally Posted by 2manysubies
FYI, I put a trans cooler only on my family beater(2001 Outback Lim) I did this because the radiator nipple for the trans cooler broke off flush(temp fix) as I was waiting on the new radiator to arrive, I noticed the car going in and out of 4th/OD, the trans would not stop doing this unless the fluid got hot, radiator replaced, no more issues. As Max Cap said, in conjunction with the stock cooler, not stand alone.
Question, did you account for the extra volume the cooler requires? If you didn't then there was your problem.