Two problems related to transmission failure have been reported for the 2018 GMC Sierra 1500. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2018 GMC Sierra 1500 based on all problems reported for the 2018 Sierra 1500.
Hard shifting that started around 40000 miles and has progressively gotten worse. The same thing happened to my 2017 Chevrolet silverado 1500 and at 90000 miles that vehicle's #3 sensor in the transmission failed. It appears this vehicle is on the same path. The transmissions in these vehicles are trash. It happens in lower gears.
The transmission failed at 32,000 miles slipped so bad could hardly drive it home on highway i95 jacksonville florida. Finally got a dealer appointment after over 2 weeks of waiting without the use the vehicle. They replaced the fluid and said it was now good. Still tends to slip I asked why they were not replacing the whole unit said no need as my warranty is almost up?.