My auto transmission only shifts up from 2 gear when its cold. If I floor it when warm it wont shift beyound first gear. The kickdown is disconnected. I just had the valve body replaced and changed the K1 and K2. The atf fluid and filter are new. Dexron III. Atf level is more or less on the max level with hot transmission. It could have been a hunch less oil in it. It does not respond to any bowden cable adjustments. Cable is not broken.

My mechanic advised me to hit the transmission from behind with a hammer or so. To get stuck or hanging parts moving again. Does this make sense? Could it be a stuck valve or so?