Saltybeach75

This is my exact issue! Purchased a 2021 3.0 Duramax with 10 speed transmission in February. Noticed the shudder at highway speeds shortly after (60-80+mph). First dealership - first visit replaced torque converter and said all was good (13 days @ dealer). Shudder was still present on trip home from dealership. First dealership - Second visit stated bad fuel and I just needed to drive all the bad fuel out, stated they would check fuel filter (17 days @ dealer). Got truck home, pick up ticket did not mention fuel filter being checked. No visual signs fuel filter had been checked either. I changed fuel filter myself, found internal mesh liner had pulled away on fuel filter. Shudder still present. Took truck to driveline specialist who did not feel the shudder was due to torque converter, transmission or drive shaft. He felt it was an engine issue, misfire, possibly fuel injector. Took truck to Second dealership - first visit explained issue and showed him fuel filter I took off. They found metal particles in fuel filter housing and on magnet. They replaced fuel pump and flushed fuel system (2 days @ dealer). Shudder present on trip home. Did test drive with tech with diagnostic laptop plugged in, no issues found with fuel injectors. Found transmission to be failing specifically 5th and 6th gears, rebuilt transmission ordered and installed (4 days @ dealer). Shudder present on trip home from dealer. Literally about to trade this truck in!!! Could this be a bad rebuilt transmission? It shifts fine, I don't feel that is truly the issue. I'm currently researching for faulty sensors or turbo issues, ect. Surely someone out there has found the fix for this issue.