This vehicle has a severe transmission shift issue that will likely cause an accident at some point. This vehicle has an Allison 10 speed transmission and began shifting extremely hard or violently from 7th to 8th gear in November of 2023. This problem began when pulling a travel trailer that is weight rated well below the capacity of this truck. This hard shift causes vehicle occupants to lunge during the event and it is feared that a catastrophic failure will occur, resulting in a vehicle accident. The vehicle was taken to the dealership where purchased as it is still under manufacturers warranty, and in March of 2024 the dealership performed a software update and transmission re-learn which solved the issue until the truck was used to pull a travel trailer again. The issue returned in November of 2024. The truck was returned to the dealership for follow up but the dealership has not taken any further action to resolve the problem at this time. There is a service bulletin (N242467600) issued from GM that seems related to this vehicle but Ive received no notification that this vehicle is eligible for transmission replacement under this service bulletin. This issue will likely result in a personal injury or vehicle accident at some point.