checkout my thread. I have more miles on my truck than most.
long story short there is no fix for this, the new trucks have shitty transmission tuning. mine got so bad it ended up screwing up other stuff and I had to have my transmission replaced (after they replaced pretty much every part inside and it wasn't fixed.)
my trans went out at ~93k miles. I never towed heavy just a lot of highway driving for work. I think they tell you its normal or you dont have the most up to date tune because they honestly have no idea whats wrong and hope that your truck goes out of warranty before any expensive repair is needed. my truck has 115k now, im going to start saving for a transmission