Hard shifting in 2 to 3 gear on 1999 automatic Subaru Forester

I have a 1999 Subaru Forrester automatic with 64,000 miles on it. I have always maintain the vehicle. Currently when it shifts into 2 to 3rd gear it makes a clank or click. After a while when it warms up it behaves normal. I have brought to the dealer said if it gets worse come back. I had them replace the Trnsmistion fluid and filter. Does any one else have this problem?

Do you know what the cause could be?

On a Forester forum some one was mentioning a technical bulliten about flashing ths TCM.