Lockup Shudder, Not Slippage: A 4L60E TCC Diagnostic Walkthrough
That highway-speed shudder in a 4L60E often gets mislabeled as a slipping transmission, but the torque converter clutch circuit is frequently the real culprit. Here is a scan-tool-first path through TCC solenoid behavior, PWM lockup, converter lining wear, and the parts-versus-rebuild call.