The most common symptom of a transmission filter going bad and needing changed is it takes longer than normal for the transmission to automatically shift gears.
If you're pressing on the gas and it takes 2 or 3 minutes for the gears to shift then your transmission fluid is either low or your transmission filter needs changed.
Your automatic transmission should automatically change gears in less than a few seconds as you accelerate and if not your transmission is either going bad, the transmission filter is clogged or you're low on transmission fluid.
Transmission filters and transmission fluid should be changed every 2 years or 30,000 to 40,000 miles and if your transmission fluid smells burnt then your transmission fluid needs changed.
You should change automatic transmission fluid every 2 years or every 30,000 to 40,000 miles or whichever comes first.
Most people know to change their engine oil every 3,000 miles or so but not many people think about changing their transmission fluid.
But changing your automatic transmission fluid and filter every 30,000 miles or so will help extend the life of your automatic transmission and keep the automatic transmission shifting properly and prevent breakdowns.
Even if my automatic transmission fluid hasn't reached 30,000 miles I'll still change it before then at around 15,000 miles or so.
That is especially true if I'm planning a long road trip as I do not want anything to go wrong and cause a breakdown so I go over the vehicle and do a lot of preventative maintenance.