you'll get a lot of different opinions, but mine is this... your trans is not new and there's going to be particles/ crap in the fluid. it has been operating under that consistency and pressure. put in new fluid, and you're completely changing that pressure and flow. that's why a lot of people do a flush on a shaky trans and it only seems to accelerate its death. just do a filter change. then you still have some old stuff in the car. kinda like changing the water in a fish bowl, you need to keep some of the old water in. just my logic on it

DO NOT FLUSH!It is a big no no,the dirt get pushed back and get stuck into the valve body.The flush with the machine uses more fluid.Change the fluid and filter.But if you want a flush,the is what you do:Remove the bottom transmission line of the radatior and point or put a hose extension on the line in a pan.Start the car up and start pouring fluid in until it is clear.This is the better way to flush an automatic transmission and gets rid of the dirt and crud.The flush machine uses more fluid and does more transmission "damage". I had to replace one transmission because it was flushed and was acting up after being flushed with the machine.My father knows a guy that has his own transmission shop and cleans valve bodies because the transmission was flushed.The complaint is:does not shift right and shifts right after the valve body is cleaned out.Did the fluid have a stinky smell to it?,if that is the case rebuild it.