Transmission Gear Slipping problems of the 2018 GMC Sierra 1500

I have a 2018 GMC sierra denali, when the vehicle is cold, usually first thing in the morning, the truck starts out in first gear and then feels like it lacks power or transmission is slipping and then bangs into 2nd gear. The more I drove the truck the worse it got. While driving down the road there is a vibration within the truck. The faster you go the more of a vibration you feel. During the vibration the steering wheel is not shaking and when you let go of the wheel the truck stays straight, so it's not the front end. Took the truck to the dealership where it was purchased, pellegrino GMC, which is a 30 minute drive and they couldn't duplicate the problems. The service advisor was advised prior to my appointment, that the banging into gear only happens when its is cold. He advised me that what I was feeling was a normal shift for my truck. I advised him about the service bulletins and he stated that it didn't pertain to my truck. The mechanic test drove my vehicle for 13 miles and didn't feel the vibration. He checked the engine codes and found none. I have had the truck a little over a year and it has 6000 miles on the odometer.

I experienced failure of the transmission to sift up or down on several occasions between 11/01/2019 and 11/11/2019. On 11/08/2019 I was monitoring the transmission temperature, and when the transmission temp reached 164 deg, the transmission would stop shifting properly at 25 to 30 mph, and the trans temp would jump to 192+ deg. Transmission seemed to slip and the vehicle would not accelerate. Rpms jumped to 3k-4k rms but speed would not change up or down. Contacted the dealership and made an appointment for 11/11. On 11/11 I drove the to the dealer 10 miles away. I monitored the trans temp as I drove, and no shifting issues until just before reaching the dealership (trans temp had reached 154 deg). I road with the dealer rep for a test drive and he was able to duplicate the problem at 30-mph and trans temp quickly rose again to over 192-deg. Dealer rep tried to use the manual shift option but even using that he was unable to get the transmisson to shift properly ans engine rpms exceeded 5k and stayed there until the transmission shifted into gear. Dealer rep stated that is not good during the test drive. Arriving back at the service department the dealer rep that test drove the vehicle told the service dep amanger the vehicle was not safe to drive. I was told the transmission would need to be torn down to figure out what the problem was and it might be after the first of the year before they would have it fixed due alack of parts due to the recent strike, and a bag log of vehicles already waiting repair parts. Other complaints that seem to match mine are NHTSA ids: 11193281, 11230193, 11221668, and 11205523. Issue is a serious safety issue if the vehicle cannot accelerate safely to merge with traffic.

While the truck is in motion and when accelerating around 15-20 mph the transmission will sometimes "hunt" for a gear causing the truck to not accelerate. This results in a mild jerking of the truck when it is trying to accelerate and feels like the transmission is slipping/skipping. This is more apparent when going up a grade versus on a flat surface. So I have to push harder on the gas pedal waiting for the truck to shift. This is a safety issue since when not properly accelerating into traffic, an accident is more likely to occur. I see that this issue has already been reported in another incident on your website. I have had this issue since I bought the truck on 02/2018 and the reason I have waited to report is due to the dealer stating to allow the computer to update/learn your driving habits. I have 11,000 miles on the truck now and still experiencing the issue.

Brand new 2018 Sierra 1500 z71. When driving the truck for the first time after sitting for a number of hours (6+hrs) the truck experiences a "hard" 1-2 shift. This occurs 100% of the time when I leave for work in the morning. Sometimes it feels like the transmission slipped, this is the hard shift feeling. Other times the truck loses acceleration, cuts out, feels like the truck has ran out of fuel. Only happens when the truck has been sitting for a long period. When I took the truck in to have this looked into I was told this is a known issue without a resolution. Ive attached a scan'd copy of the document they gave me #16-na-361.