After having simple oil and filter, and engine and cabin filter replaced at Alpine Buick GMC in Colorado Springs, CO, I received my vehicle back and noticed a complete difference in performance. It hesitates when accelerating, stays low in every gear, and bounces, and I mean bounces hard, when shifting gears, especially slowing down. When slowing down, as it shifts to the next lower gear, it almost pushes the truck forward against me pushing the breaks. Then, when feathering to accelerate slowly, it almost bounces back up to speed, hesitating until I let off the accelerator pedal a little, and it immediately shifts to about 1000 rpm in gear. I have to push really hard for it to go up a gear, and when it does, it has lost all power. My vehicle doesn-??t run right anymore after my service appt. I have brought it to my hometown dealership and they say it runs fine and nothings wrong. But there is something wrong with it.

- Winter Haven, FL, USA

Transmission shifting is at times confused causing the vehicle to jump forward shifting to first gear. It pushes your vehicle 2-5 miles an hr faster when slowing down. The transmission also does the opposite when letting off the accelerator, shifting fast to a lower gear slowing the vehicle down quickly in a jerking motion at times. I have an 8 speed transmission. GMC dealer is replacing my torque converter, stating this may fix the issue, but it is a safety concern.

- Van Buren, AR, USA

1 June 2022, while driving, started hearing a clicking noise from front end, under hood. Took to local GM dealer, Mechanic drove with me, and he heard the noise, said he would order a part and safe to drive. So, I went home. 2 June 2022 started same vehicle, a very loud banging, clicking, shuttering noise from under hood, I took back to same dealer, Dealer said collapsed valve lifter. GM service notice says for dealer to fix under warranty. Apparently, a known problem with MANY 2021 GMC 5.3 L engines. PLEASE MAKE GM RECALL THIS ISSUE FOR REPAIRDS

- Jacksonville, AR, USA

8 lifters in my vehicle needed to be replaced. While driving my vehicle (12/4/21), after the auto stop feature was activated my truck experienced a lack of power and hesitation. I then turned the truck off and upon starting it was making a knocking noise. I immediately checked the oil as I wanted to make sure there was oil in the engine. I had warning lights on the dashboard and drove it about 3 miles to the dealer to be repaired. While driving it to the dealer, it did not sound right and shook. I also experienced a lack of power and was concerned for the vehicle to stall out while in traffic. The dealership informed me this is an issue with the 2021 GMC Sierra with a 5.3L V8 engine. I had seen online that GMC issued a service bulletin to have the lifters replaced in the 2021 GMC Sierra that were on the lot before they were sold (early December 2021). If this is a known issue why weren't the lifters replaced in vehicles on the road before the ones sitting on the lot. 8 lifters were replaced by the dealership but there was a shortage of parts due to the nationwide problem. There were no warning lamps, messages prior to the failure. The only symptoms I had was shaking and lack of power as indicated above after the autostop feature was activated. I then drove about 2 miles and went into a store before coming out and having the loud knocking on startup followed by warning lights and messages.

- Saegertown, PA, USA

When shifting into drive after reversing, truck will occasionally do a small thud and hesitate to move forward. This is from a stopped position after reversing, then braking, putting the truck into drive, then it happens when starting to move forward at very low speeds (I would say about 1-2mph). Vehicles recovers quickly, however it seems like a transmission mount or something may have issues. If another car were coming up quickly, or started going expecting you to start moving, the delay the thud and hesitation causes may be enough to cause a minor incident (assuming no high speed traffic coming up behind someone as they reversed out). This issue does NOT occur every time. I have owned the truck for 4 months, and it has happened only about 4-5 times in total.

- Lithia, FL, USA

Can turn vehicle off while in gear (drive specifically). When you let off the brake, the truck acts as if it is in neutral. Discovered in my driveway when accidentally forgot to shift into park when I pulled in and pushed the stop button. Truck turned off, which would only expect if in park (or neutral), let off brake, and it began quickly rolling backwards as if it was in neutral. Fortunately the brakes were working, but had any children been riding a bike on the sidewalk or walking by, my truck may have hit them. Had I been more distracted and not noticed initially, it could have rolled into the road and hit my neighbors truck. This behavior can be reproduced every single time, and I can easily supply video.

- Lithia, FL, USA

Prior to this incident I had lifter failure on my 2021GMC SierraAt 8464 miles, I was on my way to work and I heard a loud bang and I had to pullover off the highway, my dad had to come all the way out To get the vehicle because it had major engine damage and it was on a holiday so no one would come help me.The vehicle was in the shop for over a week getting these repairs done, upon receiving vehicle it had been a week and I received service four-wheel-drive messages on the dash.Trying to use four-wheel-drive after this was a no-go every time I push the button nothing would happen it would stay in two wheel drive.After this I made an appointment with the dealership for this issue to be fixed, as I was going to get readyTo leave again with the truck having no issues other than what I-€™ve stated when I went to go start the truck nothing happened at all every light lit up on the dash and part of me thinks it-€™s an electrical issue but the Other part of me thinks the motor is locked up. Also the lights would not shut off when I turn the vehicle off so I-€™ll have a dead battery in the morning.

- Holly, MI, USA

THE CONTACT'S FATHER OWNS A 2021 GMC SIERRA 1500. THE CONTACT STATED THAT HER FATHER WAS DRIVING AT AN UNDISCLOSED SPEED, WHEN THE VEHICLE STALLED. THE VEHICLE STALLED THREE TIMES ON THREE SEPARATE OCCASIONS AND WAS TAKEN TO THREE DIFFERENT DEALERS. THE VEHICLE WAS FIRST TOWED TO Bill Kay Buick GMC (2300 Ogden Ave, Downers Grove, IL 60515) AND DIAGNOSED AS BATTERY FAILURE AND REPAIRED HOWEVER, THE FAILURE RECURRED. THE VEHICLE WAS THEN TOWED TO Phillips Chevrolet of Lansing (17730 Torrence Ave, Lansing, IL 60438) AND DIAGNOSED THAT THE TRANSMISSION CABLE CAUSED THE FAILURE. THE VEHICLE WAS REPAIRED HOWEVER, THE FAILURE RECURRED AFTER GETTING THE VEHICLE BACK FROM THE DEALER. THE VEHICLE WAS THEN DRIVEN TO Zeigler Buick GMC of Lincolnwood (6900 McCormick Blvd, Lincolnwood, IL 60712) BUT WAS NOT YET DIAGNOSED NOR REPAIRED. THE MANUFACTURER WAS MADE AWARE OF THE FAILURE AND A COMPLAINT WAS FILED. THE CONTACT WAS INFORMED THAT THE DEALER WANTED TO REPAIR THE VEHICLE. THE FAILURE MILEAGE WAS 3,000.

- Normal, IL, USA

Transmission shifts hard when shifting up and when downshifting. Vehicle jerks when going speeds <40 after coming off highway at highway speeds >70.

- Laneville, TX, USA