Next Gen Diesel Lawsuit: GM 10-Speed Defect and Recalls

A proposed class action filed in April 2026 accuses General Motors of knowingly selling trucks and SUVs with defective 10-speed automatic transmissions that can shift violently, lose power, or lock the rear wheels at highway speeds. The GM 10-speed transmission class action lawsuit, Napa Valley G Experience LLC v. General Motors LLC, was filed on April 13, 2026, in the U.S. District Court for the Northern District of California and carries case number 3:26-cv-03148. The named plaintiffs are Napa Valley G Experience LLC, Juan Morales, and Ruben Smith, represented by Michael F. Ram, Colin Losey, and Will Ourand of Morgan & Morgan’s Complex Litigation Group.¹

Which Vehicles and Transmissions Are Covered

The complaint targets GM’s family of 10-speed automatics: the 10L60, 10L80, 10L90, and 10L1000. These units are used across a wide range of Chevrolet, GMC, and Cadillac trucks and SUVs.²

The class has not been certified, so the final scope will be set by the court. For now, the vehicles most closely tied to the underlying defect through GM’s own recall and service bulletin activity include 2020–2022 Chevrolet Silverado 1500, 2500, and 3500 diesel pickups; 2020–2022 GMC Sierra 1500, 2500, and 3500 diesel pickups; 2021 Cadillac Escalade, Chevrolet Tahoe and Suburban, and GMC Yukon and Yukon XL diesels;³ and 2021–2024 Cadillac CT4, CT5, and Escalade; Chevrolet Camaro, Silverado 1500, Suburban, and Tahoe; and GMC Sierra 1500 and Yukon covered by GM’s Gen 3 valve body service bulletin.⁴

What the Alleged Defect Does

According to the plaintiffs, the transmissions are prone to “violent or erratic shifting, delayed acceleration, and even a complete loss of motive power.”² The complaint traces the problems to instability in hydraulic pressure control and clutch timing, tied to valve body wear, torque converter contamination, and inadequate software calibration.⁵

The most dangerous failure mode is rear-wheel lockup during downshifts from eighth gear at highway speeds. GM’s own investigation identified 1,888 field reports of rear-wheel lockups between January 2020 and August 2024, along with 11 incidents in which affected vehicles veered off the roadway. Three minor injuries were reported, none from crashes.³ The complaint also notes that GM co-developed the 10-speed with Ford, whose version has drawn similar complaints in the United States and Canada.¹

Why the Complaint Says GM Knew

A central part of the plaintiffs’ knowledge case involves Next Gen Drivetrain, Inc., a veteran-owned aftermarket parts company in Lancaster, Pennsylvania that operates as Next Gen Diesel. Next Gen is not a plaintiff, but its products and findings are cited in the complaint as evidence that GM could have fixed the defect earlier.

The company, led by Nathaniel Valentin, says it identified the root cause of the defect and developed a proprietary fix as early as mid-2023.⁶ Its “Project Carbon” valve body kit replaces factory aluminum spool valves with precision-machined steel valves, removes the factory line pressure control accumulator through a process it calls PulseDelete, and installs a thicker laser-cut separator plate in place of GM’s paper gaskets and thin filter screens. The kits sell for roughly $800 to $3,500.⁷

The complaint alleges that Next Gen identified “crosslinks in the valve body” as the cause of wheel lockup and that in July 2025 a senior GM official contacted the company about buying parts. According to the complaint, GM initially declined to purchase from Next Gen, but roughly 60 to 70 GM dealerships opened wholesale accounts with the company on their own and bought between 400 and 600 kits.⁵

The Recalls That Preceded the Lawsuit

In October 2024, GM issued a stop-sale order and recalled about 462,000 diesel trucks and SUVs under NHTSA recall 24V797000. GM’s initial remedy was a software update to the transmission control module that, if wear was detected, would limit the transmission to fifth gear so the driver could pull over safely. GM acknowledged this software fix did not repair the underlying valve body defect or prevent further deterioration.⁸

The recall campaign expanded in early 2026. In February, GM added 43,732 high-end 2022 SUVs with electronic shift-by-wire under NHTSA recall 26V085.⁹ A separate recall, 26V083, covered 1,055 vehicles whose dealerships had installed the wrong version of the transmission control software during the original recall, leaving those trucks and SUVs without the anti-lockup safety feature.⁸

GM’s Gen 3 Valve Body Fix

By August 2025, GM began shipping a redesigned “Gen 3” valve body to dealerships as a more permanent hardware fix. The diesel part carries number 24071206. GM’s valve body has gone through three generations: the Gen 1 was discontinued after failures, the Gen 2 suffered from excessive bore wear, and a mid-2024 material change to the Gen 2 fixed the bore wear but introduced other issues.¹⁰ The Gen 3 is a ground-up redesign with new solenoids, new wiring, a new body, and a consolidated architecture that eliminates the auxiliary valve body.¹¹

GM formally documented the rollout in Service Bulletin 25-NA-334 on October 29, 2025.⁴ The class action complaint alleges that early field reports indicate Gen 3 units continue to fail, though those claims have not been independently verified.⁵

Where the Case Stands

The lawsuit is at an early stage. On June 5, 2026, GM filed a motion to dismiss, and a hearing is scheduled for August 5, 2026, before Judge William H. Orrick in San Francisco.¹² No class has been certified, no settlement exists, and there is no claims process to sign up for.

What Owners Can Do Now

If you drive one of the trucks or SUVs tied to the 10-speed defect, the practical steps are the same ones that protect any potential class member. Check your VIN against open NHTSA recalls, particularly 24V797000, 26V083, and 26V085, and confirm with your dealer which software version and which generation of valve body is installed in your vehicle. Keep every repair order, service invoice, and diagnostic printout related to shifting, shuddering, power loss, or wheel lockup. Save your own notes on dates and symptoms.

Lemon law claims and individual warranty claims remain available on their own timelines regardless of whether the class is certified. If the case settles or a class is certified, the records you kept will be what determines your eligibility and, in many settlements, the size of your recovery.

1
Top Class Actions. GM Class Action Alleges Defective 10 Speed Transmissions Cause Shifting Issues Power Loss
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Wards Auto. GM Recalls 462K Trucks SUVs Transmission Rear Wheel Lockup
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Duramax News. GM Confirms Gen 3 10 Speed Valve Body What Changed vs Gen 2
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ClaimDepot. GM Class Action Alleges Defective 10 Speed Transmissions Cause Dangerous Wheel Lockup
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Next Gen Diesel. General Motors 10 Speed Transmission Recall Heres How We Fixed It
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Car and Driver. Chevy Tahoe GMC Yukon Cadillac Escalade Transmission Recall
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Pickup Truck Talk. GM Releases New Gen 3 Valve Body for 10 Speed Transmission Wheel Lock Up Fix
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PACER Monitor. Napa Valley G Experience LLC et al v. General Motors LLC