I just did a transmission drain and fill this past weekend with 46k miles on my 2017 gasser. It wasn't super cheap, but I think I've set it up so that I can perform the DIY version of this a little more easily in the future: I purchased a $36 transmission oil pan with a plug (
http://a.co/d/f3kcvzM), a $17 dipstick and chart to measure fluid levels (
http://a.co/d/cAd6eQw), and a$16 infrared thermometer to get the transmission fluid temperature (
http://a.co/d/8vvbnqK).
I have to add about 5-10 degrees to the fluid temp reading while at idle in neutral, but the sensor is in the pan and I tested it on my uncle's Ram truck that has a transmission temp readout gauge on the console and it was within that 5-10 degree margin.
So, I invested about $70 in equipment to make it so I could do this on more frequent intervals without having to go to the dealership (who quoted me $250 for a flush).
I spent $30 on a filter and gasket (opted for that instead of rtv) plus about $30 for the 5 quarts of ATF+4 that I used (Walmart sells it). So, I still came out to about half price. ;-)