Home · 2025 GMC Sierra 2500 Hd · Complaints
These are the actual owner complaints behind this car’s reliability verdict, filed with the federal government, unedited. They’re unverified reports, not confirmed defects: read them as leads for your pre-purchase inspection, not a diagnosis.
3 of 24 complaints match · Transmission & drivetrain · clear filters
The transfer case leaked out all the fluid while driving over a period of time and damaged internal parts before the first oil change. This has happened 2 times now, and is currently leaking again with less than 10k miles.
NHTSA ODI 11721851
transmission locked up 8 times from 1,050 miles to current 3,885 miles. It has happens each time around 40 mph. Each time it’s like hitting the brakes. The 8th time it locked really hard like slamming on the brakes. I’m worried with winter months what will happen on snow/ice covered roads. Called dealership and was told GM refuses to do anything until it completely fails. It seems they know what the problem is but refuse to fix till the truck stops moving during complete failure. No warning lamps and dealer ship says they can’t replicate it.
NHTSA ODI 11698271
Transmission fluid overheating, which is a known issue in other GM models with 6.6L diesel with 12 speed allison transmission. Confirmed by warning message received on dashboard and transmission fluid temperature gauge. This occurred within 3 weeks of purchase. Dealer confirmed “Valve” needs to be replaced. Part is on back order with no arrival eta. Service advisor indicates the truck is not safe to drive and remains in the service department.
NHTSA ODI 11662707
Working with the data? Download all 24 complaints as CSV · fetched from NHTSA July 19, 2026