I also had a gear shift issue, mine when pulling a “heavy” (7-9k) load would lug and throw a P04db code. If you go into your transmission tuner and look into your clutch values menu, I reset mine approximately 3 times and I haven’t had an issue since. It seems as if the tune is telling it when to shift most efficiently but the trans itself doesn’t want to do they fight each other. Once truck is back home I plan to change transmission fluid and filter and reset values with fresh fluid and drive a nice long trip empty to let it relearn. My def has also increased. But if I spend an extra 4$ a month to prevent my egr from setting my truck on fire I consider it a fair trade. Def useage was normal at first and has gradually increased so my stage 2 is going to come in the next 1k miles once delete test pipe comes in!