I never flush , use only recommended OEM fluids, and never had a problem. I own a Chevy avalanche 2010, and I don’t know when the fluid was changed because no records were kept. So I had a mechanic drop the oil pan change out the filter and not flush because it could possibly force contaminates through the system where they would’ve been just laying in the pan. I also have a 2008 FJ cruiser that I took to Toyota and asked them to do the same. I made sure that they understood not to flush to use only the OEM fluids. When I got the bill, I noticed it was a little bit cheaper that I had expected so I walked over to the Parts department and asked them what fluid did they put in my FJ cruiser. They put in a non-OEM fluid because it was cheaper manufactured by God knows who. I took my next step up to the manager’s office and told him I wanted to have that fluid dumped, and the right stuff put in. After that, there was never a problem with the transmission , there never was before that either. That was two years ago and the FJ cruiser is really bad for transmission shutters problems but mine is fine. Now I have a 2014 Yukon and I plan to change the fluid in it because there are no records again kept by people who did their own work at home or they just didn’t cheap records at the mechanic shops. Again, there will not be a flush because I have no idea if a original recommended transmission fluid change was done. Don’t take my word for Google it. I don’t know if you flushed your system or just had the transmission fluid dropped and I don’t know if you had the OEM fluid put in even though you asked for it. You really gotta watch these people that do the work on your stuff.
One last thing. The reason I bought a third generationYukon Denali. 2014, because it had a tried and tested six speed transmission before they started changing them in later years