I am the original owner of a 2018 GMC Sierra 1500 with the 6.2L L86 engine and 8-speed 8L90 transmission. I began experiencing severe transmission shuddering and harsh shifting, especially at lower speeds or under light acceleration. When the issue occurs, I press the gas and the engine revs up to 6,000 RPM without reaching 20 MPH, making it extremely difficult -?" and dangerous -?" to merge into traffic or cross intersections. This issue has worsened over time and is now a critical safety concern, especially with children in the vehicle. I have researched this issue and found that many owners report the same transmission defect, and there is an open class action lawsuit and a GM Technical Service Bulletin (TSB #18-NA-355) describing the exact symptoms. The vehicle has become unsafe to drive. GMC should issue a recall or mandatory repair program for this known defect before someone is injured or killed.

- Gilbert, AZ, USA

2018 gmc Seirra 1500 8 speed transmission. Making unsafe conditions while driving transmission tends to make hard shifts, jerks, hesitation when moved into gear, gets worse when stopping momentarily at stop lights and then trying to accelerate vehicle will not move. Makes hard shift and jerks then will accelerate in an unsafe manner.

- Fort Myers, FL, USA

The speed of the truck will not increase. The rpms goes really high and the truck will not move into the next gear. The rear end of truck vibrates. I took this to the dealer and was told it is the transmission fluid is faulty. The check engine light does come on. I did not have the new transmission fluid changed because dealer said is cost $300 for the fluid and $100 for the labor and $168 for the diagnostics. So I still have the same problem. Also told you can not purchase this transmission fluid no where but GMC.

- Tickfaw, LA, USA

The truck displayed warning lights for ABS, traction control, trailer brakes, and front park assist. Additionally speed control (cruise) did not function. This presented a safety issue. I took to dealer asap. They repaired by replacing left rear wheel speed sensor. Cost about $216. Appears to work correctly at this time.

- Mt. Vernon, IL, USA

Vehicle suddenly went into Reduced Engine Power while driving in heavy traffic. Vehicle immediately began to slow down and although there was some throttle response it was difficult to maneuver through traffic to get to the side of the road. This event happened around the 31,000 mile mark. The Reduced Engine Power message came on, but I do not remember hearing an audible alert. Being a 40 year Automotive Technician for GM, I am familiar with pulling codes and replacing parts. I called the dealership to see if this was covered by warranty and was told no. After pulling the codes, I personally replaced the Throttle Body Sensor and the Accelerator Pedal Assembly, but the vehicle continued to go into Reduced Engine Power mode. I took the vehicle into the dealership and they diagnosed the cause as a corroded connector. The connector was replaced and the vehicle was returned to me. After a little over one month and less than 1,000 miles the vehicle is once again going into Reduced Engine Power mode. I can have my vehicle available for inspection if necessary.

- Howell, MI, USA

Truck shift into gear very roughly. Shakes when driving through all speeds. Feels as if something is falling off the truck.

- Little Rock, AR, USA