How often or should you change out Tranny fluid

New fluid in a neglected transmission is bad. New fluid has fresh detergent for cleaning. The new fluid can not absorb enough built up dirt particles. New fluid can easily break a neglected transmission. New fluid in a consistently serviced transmission will extend the life.

If your transmission ever gets hot. Change fluid immediately regardless of date of previous change. I think the magic number is 250deg? Above that temp immediate change required.