general problems of the 2017 GMC Sierra

Vehicle has hard shift at 5-6 mph. Dealer stated could not find issue, and reflashed tcm. Approx month later, at 10k miles, truck hard shifted from red light on highway, once up to 45 mph, shutdown. Steering wheel locked up, no brakes, no control of vehicle at 45-50 mph. Dealer kept for one week, stated loose cable on starter from battery. Exactly 1k miles later (5 weeks), now at 11k miles, truck hard shifted at 5-6mph, and at 45-50 mph truck tried to shift in 4wd. All lights on dash came on as a result. Dealer has currently had the truck for two weeks and can not find issue. They supposedly consulted gm, and instead of sending an expert tech to help dealer find issue, advised dealer to replace ecm. Replacing ecm is the general answer to not sure what is wrong. This truck is a safety issue, as when it shuts off going 45-50 mph there is no control or brakes operational on the vehicle. Gm will replace the ecm, and just like right now, will not be able to replicate the problem, and expect me as the consumer to take delivery back of the vehicle. Currently all of my documentation is in the dash of this truck, at the dealership. Trying to determine how myself as the consumer can help ensure this safety issue is corrected, and not passed on.

The stabilitrak sensor keeps going on and off. I've had this issue when I first got the truck in the end of October in 2017. The dealership could not fix it at first but finally had to fix some wiring. I've seen it go on a few times since then but never stayed on. And for about 2-3 weeks it's been coming on and off but staying more on and not going away now. I feel like this shouldn't happen to a newer truck.

Vibration 65+ mph, felt in steering wheel and seat. Steering wheels quivers at 65+ mph. Truck feels very unstable at highway speeds. Dealer states it's normal.