When your transmission isn't shifting properly it will need to be seen to diagnose to determine if it is just a fluid issue or if something else has happened. The best way to prevent transmission issues is to have it serviced on a regular basis. That means fluid services every 30,000-50,000 miles. It should be serviced by a reputable shop to make sure it has the correct fluid, the wrong fluid can cause just as much damage as not having it done at all. Transmissions have gotten more complicated as technology has increased, with that the fluids are more specific.
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