Shudder

In most cases once you have transmission symptoms or abnormal behavior the damage is already done. A flush or service may help but the idea is not to let it get to that state. IMO even 30k is too long. Fluid should come out in a transmission service like it went in with no discolor, clean, with no sign of oxidation or being burnt from heat. If it does not look like this or is burnt, discolored and oxidized the damage/wear has already happened. If you work a truck and tow like most of us with RV’s you should be changing fluid in most cases every 15-20 k with 20 as the max. I personally change transmission fluid at 15k in all my vehicles. I know many will say this is over kill and many times they are the same folks that wait for the abnormal performance or in this case a “shutter” as a reminder to service their vehicle. Like all things mechanical the most cared for transmission can fail at any point in its life. In most cases if you cut the recommended intervals in half you will wear out the rest of the vehicle long before the drive train. A happy transmission is one that is filled with like new fluid its entire life. Every 30 k is recommended for normal driving. Towing an RV is exempt from this.