Today's transmissions have multiple solenoids that vary in cost and procedures. While codes tell us where to start looking and diagnosing what is wrong with your vehicle and seldom identify the actual problem. A shift solenoid code could be a bad solenoid for sure, but it could also be: wiring, connections, a hydraulic fault or a mechanical fault.
A good rule of thumb is every three years or 26K miles. Many manufacturers state that their fluid is a lifetime fluid and never requires changing. This gimmick to present their cars as low maintenance is misleading and will reduce the life expectancy of your transmission.
We recommend servicing your transmission. When you flush a transmission, all you are doing is exchanging the old fluid for new. The pan does not get dropped and the filter does not get changed. The old fluid must pass through the filter before it gets to the flushing machines, so any debris never gets removed. When you service your transmission, the pan gets dropped, we can monitor and note the type and amount of debris that is collecting, the filter gets changed, and we can make any necessary adjustments.