Typically hard shift points are caused by something sticking or binding in the valve body and it may or may not set a DTC and turn on the SES light. It could be a shift solenoid, a spool valve or a check ball binding in a worn orfice in the valve body spacer plate. Changing the fluid and filter should be done regularly around 36,000 miles and it's inexpensive compared to transmission repairs. A lot of times it will take care of symptoms like you're experiencing, if not, a visit to a reputable transmission shop will be in your future
