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Rough Shifting & Hesitation on my 2019 Sierra 1500 - Is this normal?

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Paul Z. · rep 0 · May 22, 3:48 AM · 1 replies · solved · Question

Vehicle: 2019 GMC Sierra 1500 SLT

Hey everyone,

I've got a 2019 GMC Sierra 1500 SLT with the 5.3L V8 and the 8-speed automatic transmission. Lately, I've noticed some really rough shifts, especially between 1st and 2nd gear, and sometimes a noticeable hesitation when accelerating from a stop.

It feels like the transmission is clunking into gear, and it's not a smooth experience at all. It's got about 60,000 miles on it now. I'm worried this could be a sign of a bigger problem.

Has anyone else experienced this with their 2019 Sierra or similar GMC trucks? Is this just how these 8-speeds are, or should I be concerned about a potential issue? I'm trying to figure out if this is something I need to take to the dealer immediately or if there are common fixes or TSBs for this.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:48 AM

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ClearTheCode admin answer:

It sounds like you're describing a common concern with the 8-speed automatic transmissions (8L90/8L45) found in many GM trucks and SUVs, including your 2019 GMC Sierra 1500. This issue often manifests as harsh shifts, hesitation, or a 'clunking' sensation, particularly at lower speeds or during light acceleration.

Here's what you should know:

  1. Causes:

    • Transmission Fluid Degradation: The original transmission fluid used in some of these units can break down prematurely, leading to friction material issues and rough shifting. GM later released a new fluid (Mobil 1 Synthetic LV ATF HP) to address this.
    • Torque Converter Issues: In some cases, the torque converter itself can be a source of shuddering or harsh engagement.
    • Software Calibration: Transmission control module (TCM) software can sometimes contribute to shifting characteristics, and updates are often released to refine shift points and feel.

  2. Diagnostics & Potential OBD Codes:

    • While rough shifting might not always trigger a check engine light immediately, if the issue worsens or causes significant slippage, you might see codes like P0700 (Transmission Control System Malfunction) or codes related to specific gear ratios or solenoid performance.
    • A professional scan tool can often reveal pending codes or specific transmission data that points to the root cause.

  3. When to See a Shop:

    • Immediately: If you experience significant loss of power, a complete failure to shift, or a check engine light illuminates with transmission-related codes.
    • Soon: Given your description, it's highly recommended to have a qualified GMC dealership or an independent transmission specialist inspect your vehicle. They can check for relevant Technical Service Bulletins (TSBs) that address these known 8-speed transmission issues.

Many owners have found relief through a transmission fluid flush and refill with the updated fluid, and in some cases, a torque converter replacement or TCM reflash. Don't delay, as continued harsh shifting can accelerate wear on other transmission components.

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