there is nothing wrong with changing your transmission oil and filter- i do it every 30 thousand miles cause your filter starts to stop up with fine clutch shavings. after 30,000 you can pull your oil pan off and scrap about 1/16 of and inch of clutch shavings with your finger. so you know its in the filter if its settled in the pan also. i’ve heard of people putting pure synthetic oils in there trans, and the car woundnt even move cause the clutchs slip to easy due to the oil is to slick- trans fluid is kinda dry when you feel of it, i guess so the clutchs plates can grab better. it is good to change your trans fluid, cause heat will break down any oil over time. oil would last a lifetime if the heat wasnt breaking it down.
You are doing what I do....replace the filter and what is in the pan.
The lube shops are selling a ‘total fluid exchange’.
Say you replace 4 quarts when you drop the pan...there may be another 7 in the transmission...they are trying to scare people into exchanging all of this fluid.
I have operated on the notion that changing out some of the fluid with every filter change will be sufficient...but apparantly some new cars don’t even have changeable filters and pans.
I would never do the ‘transfusion’ the shops offer...seems like alot of stuff can go wrong.