Brandon Sloan is a GM Master Automotive Technician, transmission rebuilder, and content creator operating out of South Carolina. The mechanic has one million followers on TikTok, where he shares customer stories and insights under the handle @performancetransmission. He recently filmed a 2025 GMC Sierra that showed up at the shop with a shocking oil leak. 

Customer states, “I’ve got an oil leak at 3,800 miles”

The owner brings in their brand-new GMC Sierra pickup stocked with a four-cylinder TurboMax engine and GM’s updated 8L80 eight-speed transmission.

Sloan filmed it in the parking lot, warning viewers, “And it’s not gonna look pretty.”

He’s right: a peek under the front of the truck proves the customer complaint to be true. It’s literally dripping oil onto the ground. Not to mention the noise.

The 2025 GMC Sierra comes standard with a 2.7-liter TurboMax engine that looks great on paper

It’s a turbocharged four-cylinder that puts out 310 horsepower and 430 lb-ft of torque. GM designed it to deliver V8-style pulling power while saving fuel. It tows up to 9,500 pounds when properly equipped. Despite the size, it’s built for hard work. But some owners aren’t seeing it deliver.

Some mentioned real-world power can feel flat at times, even with all that torque. One GMInsideNews.com forum user noted the truck reads swell enough on a spec sheet, but that initial acceleration and fuel economy really disappoint compared to the DuraMax. “It just feels like it’s straining under throttle,” one said. “So slow compared to my brother’s 2.7L EcoBoost, hugely disappointing. It’s an embarrassment.”

On top of that, some owners report infotainment bugs that cause the center screen to freeze randomly. A small glitch, but a frustrating one when you’re relying on it for towing data or navigation.

Now, you have to consider the TurboMax for what it is: a single Sierra engine option among four total. Drivers can also pick a 5.3L EcoTec3 V8, a 3.0L Duramax Turbo-Diesel L6, or a 6.2L EcoTec3 V8. These are decidedly more “appropriate” for those who wimper about the four-cylinder’s lack of oomph under throttle.

Paired with the TurboMax is GM’s 8L80 eight-speed automatic transmission

It’s built to handle torque and heavy towing. You’ll also find it in some of GM’s full-size V8 SUVs and trucks. It’s a tough box, at least on paper.

In practice, though, it’s drawn its own set of complaints. Some say the transmission tuning feels off. It tends to hunt for gears or hesitate during downshifts, especially under load. 

Drivers have reported clunky or delayed shifts, mainly during stop-and-go traffic or when towing. Some say the transmission feels like it’s fighting itself, constantly trying to balance power and fuel efficiency, but never quite doing either smoothly.

At higher mileage, there are reports of valve body issues and long delays getting parts for repairs. Again, it’s the kind of thing that wouldn’t feel as concerning if GM hadn’t earned a reputation for patch jobs over long-term fixes.

All of this would raise fewer eyebrows if GM didn’t already have a rocky track record with quality control

The company recently recalled nearly 600,000 trucks with the L87 6.2-liter V8 due to crankshaft and bearing failures. Engines were seizing. Some drivers lost power on the highway. 

In many cases, GM’s solution wasn’t to rebuild the engines. It was to switch to thicker oil and send folks on their way. That doesn’t exactly build confidence.

And this Sierra isn’t helping. The comments flew in:

“2.7 in a full size pick up. WTF”

“GM really has quality issues. I don’t understand why people keep buying them?”

“Had one a few months ago rod number 2 checked out at 67,000 then they goodwilled it said something about gm may be extending powertrain to 100,000 on those.”

“I’d say that’s what happens when you add an over-stressed four cylinder to a full-size truck, but apparently, they’re even having problems with the V8s.”

“I have a 2024 Chevy Silverado with that motor and I received a letter yesterday from gm with the vin number and and just wondering if those motors are going to be in a recall to.”

“Think it’s time to take a flatbed to the dealership,” one remarked coyly. Sloan replied directly to that one directly: “That’s exactly what he did.”

MotorBiscuit reached out to @performancetransmission via TikTok direct message for comment.