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2018 Sierra 1500 Transmission Fluid Change - When is it due? Shuddering issues.

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Mark S. · rep 0 · May 22, 3:45 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

Hey everyone, I've got a 2018 GMC Sierra 1500 SLT with about 85,000 miles on it. Lately, I've noticed a slight shudder, especially when accelerating from a stop or at lower speeds, sometimes around 30-40 mph. It's not constant, but it's definitely noticeable.

I'm wondering if it's time for a transmission fluid and filter change. The dealership told me a while back that it's 'lifetime fluid,' but I'm skeptical, especially with these miles and the shuddering. What's the recommended interval for these trucks, and is this shudder a common sign?

I've heard about some issues with the 8-speed transmissions. Any advice on whether this is a DIY job or strictly a professional one? I'm pretty handy but haven't tackled a transmission service before.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:45 AM

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The shuddering you're experiencing in your 2018 GMC Sierra 1500 at 85,000 miles is a common concern, especially with the 8-speed automatic transmissions (8L90/8L45) used in many GM trucks and SUVs. While some manufacturers refer to transmission fluid as 'lifetime,' this typically means it's designed to last the expected life of the vehicle under normal operating conditions, which often doesn't account for severe duty or extended mileage.

Here's what you should consider:

  1. Transmission Fluid Service Interval:

    • For your 2018 Sierra, GMC generally recommends a transmission fluid and filter change every 97,500 miles (150,000 km) for normal service. However, if you frequently tow, haul heavy loads, drive in mountainous terrain, or operate in extremely hot climates, the severe duty schedule recommends service much sooner, often around 45,000 miles (72,000 km). Given your mileage and symptoms, a service is definitely warranted.

  2. Addressing the Shudder:

    • The shudder is often linked to the torque converter clutch (TCC) and can sometimes be resolved with a transmission fluid flush and refill using the correct, updated fluid (often a specific low-viscosity fluid like Mobil 1 Synthetic LV ATF HP). A filter change is also crucial.
    • DIY vs. Professional: A transmission fluid and filter change can be a DIY job if you have the right tools, knowledge, and a clean environment. However, ensuring the correct fluid level (which often requires specific temperature ranges), using the exact OEM-specified fluid, and proper disposal of old fluid can be challenging. For a first-timer, especially with shuddering issues, professional service is often recommended to ensure proper diagnosis and fluid type.

  3. Potential Causes & Diagnostics:

    • Worn Fluid: Degraded fluid loses its lubricating and cooling properties, leading to increased friction and potential TCC issues.
    • Filter Clog: A clogged filter restricts fluid flow, impacting transmission performance.
    • Torque Converter: In some cases, the torque converter itself may be failing, requiring replacement. A fluid service is a good first step before considering more extensive repairs.
    • OBD Codes: While a shudder might not always trigger a Check Engine Light, it's worth scanning for transmission-specific codes (e.g., P0700 - Transmission Control System Malfunction, or specific TCC performance codes) using an advanced OBD-II scanner that can access transmission control module (TCM) data.

When to See a Shop: If the shudder persists after a professional fluid and filter change, or if you notice any harsh shifts, slipping, or a persistent Check Engine Light related to the transmission, it's critical to have a qualified transmission specialist diagnose the issue. They can perform more in-depth diagnostics, including pressure tests and internal inspections, to pinpoint the root cause.

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