I purchased a used 2018 Chevrolet Silverado High Country (VIN: [XXX] ) on [XXX], with 24,375 miles. On the day of pickup, the truck felt like it was driving over rumble strips. Dimmitt Chevrolet flushed the transmission and used the updated Mobil 1 HP LV fluid. This worked temporarily, but the shudder returned. CarMax then sent the truck to Burkes Transmission in Sarasota, where they replaced the torque converter. However, the shop declined to rebuild the transmission, citing its complexity. I later brought the truck to Cox Chevrolet in Bradenton. Despite clearly describing the shudder, harsh shifting, and driveline clunk, they told me the behavior was normal and refused to investigate further, stating, Well look into it once the unit fails completely. The symptoms have worsened. Harsh 1’2, 2’3, and 3’4 shifts are back. Shifting into Drive causes a loud clunk and forward lurch. Cold starts cause bucking and sudden stopping. Ive replaced the tires, Bilstein 5100 rear shocks, and front suspension parts, but the problem persists. I signed on to a class action lawsuit against GM over the 8L90 transmission, but my claim was denied. This issue is well-documented and matches reports from many other owners. It affects drivability, safety, and long-term reliability. GM and its dealers have failed to properly address this known transmission defect. I urge NHTSA to investigate further. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)