Hello, I have 88k on my 2018 Max Limited. I've always had weird or erratic shifting (since I bought it with 55k in 2020 from the auction) much like what most of you are describing in this post....anywhere from shuddering, slipping and delayed shifting especially from Park to Reverse. I used to have a hard bump when downshifting from 5th to 4th gear. When I did a rear differential service at the ford dealer at 80k sometime last year, the hard bump went away. I recently decided to have the full transmission service at the ford dealer around 87k miles in Feb 2023. For the first several weeks, I had very bad transmission activity, pretty much everything I described above. About two weeks later I asked the dealer if they can clear the memory so my tranny can re-learn and they said no, they said the tranny is always learning and will adjust as needed. I went camping the next weekend (third week after service) towing my travel trailer (around 6k pounds) and still had the same weird behavior. About the 4th week, we went to Disneyland and the transmission started overheating on the freeway, I noticed smoke coming from under the car, I smelled transmission fluid instantly and pulled over. I thought for sure my tranny was toast. I had the car towed to the same ford dealer and they diagnosed for free (I have no warranty) since they recently did the tranny service. It turned out that the dealer overfilled my tranny by 1+ quarts. Not sure how that could've happened if they used an automated machine. They offered to fix at no cost, they refunded my money for the tranny service, and they said the fluid is at the right level now, they cleaned the tranny cooler and the underside of the car and now the car shifts soooo much better. It's been six weeks (2 weeks after the dealer fixed their mistake) and I have smooth shifting, no slipping, very little to no shuddering and I can barely feel it shifting from P to R. My advice is don't wait until 100k or after to service your diffs and tranny. Do it early and you may have a better experience driving your car.
On another note, regarding taking the car to the dealer without a code, I would still take it in as early as possible. The more documentation there is at the earliest possible mileage, the better. I was lucky enough to get my previous SUV on the lemon law buy back for various recurring issues. But one thing I noticed is that the money I got was based on the amount of miles I drove with the issues. For example, if you start complaining around 80k and you get lemon buy back at 90k, they'll only cash you out based on 10k miles of ownership. I don't know how they calculate it but there is some prorated formula they use. However, if you start complaining at 20k and you get lemon buy back at 90k, then you get cashed out based on 80k miles worth of ownership. Moral of the story is take it in when you have any issue, with or without a service light.