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What transmission is in a Chevy 2500 6.6 gas?

The Chevy 2500 6.6 gas model is equipped with a Hydra-Matic 6L90 six-speed automatic transmission. This transmission is designed to provide smooth and efficient power delivery for the 6.6-liter Vortec V8 engine found in the Chevy 2500 series trucks.

Overview of the Hydra-Matic 6L90 Transmission

The Hydra-Matic 6L90 is a heavy-duty, six-speed automatic transmission developed by General Motors. It is designed to handle the high torque output of the 6.6-liter Vortec V8 engine, which is rated at up to 464 lb-ft of torque. The 6L90 transmission features a wide gear ratio spread, allowing for efficient power delivery across a variety of driving conditions, from towing heavy loads to highway cruising.

Key Features of the 6L90 Transmission

Six-Speed Design: The 6L90 transmission has six forward gears, providing a wide range of gear ratios for optimal performance and fuel efficiency.

Torque Converter: The transmission uses a torque converter to transfer power from the engine to the drivetrain, providing smooth and seamless acceleration.

Electronic Controls: The 6L90 is electronically controlled, allowing for precise shifting and adaptive programming to match driving conditions.

Towing Capability: The transmission is designed to handle the high torque and weight requirements of towing, making it well-suited for the Chevy 2500's capabilities.

The Hydra-Matic 6L90 transmission is a robust and capable unit that complements the power and capability of the Chevy 2500 6.6 gas model. Its advanced design and features ensure smooth, efficient, and reliable power delivery in a wide range of driving scenarios.

How do I know if I have a 6L80 or 6L90?

The main ways to identify a 6L80 from a 6L90 are by the RPO code (6L80=MYC, 6L90=MYD), the length, and the pan shape. The 6L90 is a heavier-duty version that is approximately 1-3/8 inches longer and has a pan with a flatter corner, while the 6L80 is shorter and has a more rounded pan corner. You can also check the part numbers or look at specific internal components if you have the transmission disassembled.

This video explains the difference between 6L80 and 6L90 valve bodies: 57sBrad's TransmissionYouTube · Apr 24, 2024
Key identification methods
This video shows how to identify a transmission by using the gear selector on the dashboard: 52sCodemans autoYouTube · Nov 2, 2023

RPO Code: Look for the RPO (Regular Production Option) code on the glovebox or vehicle service tag.
- MYC: indicates a 6L80.
- MYD: indicates a 6L90.
Transmission Length: The 6L90 is longer than the 6L80.
- 6L80: Case with bell housing length is approximately 23.5 inches.
- 6L90: Case with bell housing length is approximately 25 inches (1-3/8 inches longer).
Transmission Pan: The shape of the transmission pan is a reliable indicator when the unit is out of the vehicle.
- 6L80: The pan has a rounded corner on the back.
- 6L90: The pan has a flatter corner on the back.
Part Numbers: GM part numbers for transmission parts often begin with 242. The specific part number on the TEHCM sticker (under the transmission pan) can help identify the exact model and year.

This video discusses the size differences between 6L80 and 8L90 transmissions: 1mSwap TimeYouTube · Feb 19, 2020

What transmission does the 6.6 gas have?

The "6.6 gas" refers to GM's 6.6L V8 gasoline engine, most commonly paired with a 10-speed Allison automatic transmission in models like the Chevrolet Silverado and GMC Sierra 2500/3500 HD. The engine produces 401 horsepower and 464 pound-feet of torque, with the 10-speed transmission designed to improve acceleration and performance. While some older models may have a 6-speed transmission, the newer combination with the 10-speed transmission is generally well-regarded for its durability and towing capability.

You can watch this video to learn more about the 6.6L gas engine and its new 10-speed Allison transmission: 59sGetty's GarageYouTube · Apr 1, 2024
Engine specifications and features

Engine: 6.6L V8 (L8T) naturally aspirated gasoline engine.
Horsepower: 401 hp.
Torque: 464 lb-ft.
Construction: Durable, with a cast iron block, forged crankshaft, and aluminum heads.
Valve Train: Simple pushrod design with hydraulic roller lifters.
Key features: Variable valve timing and no cylinder deactivation.

This video provides a closer look at the engine's features and design: 48sGetty's GarageYouTube · Oct 30, 2025
Transmission specifications and features

Transmission: 10-speed automatic transmission, which is a different, lighter-duty version than the one paired with the diesel engine.
Performance: Designed to improve acceleration and help the engine operate in more optimal power bands.
Shifting: Seamless, sequential shifting without skip-shifting.
Cooling: Some users report the transmission stays cool while towing.

This video explains the difference between the 10-speed transmission used with the gas engine and the one used with the diesel engine: 1mGetty's GarageYouTube · Mar 24, 2024
User experiences and reliability

Towing: The engine and 10-speed transmission combination is frequently praised for its towing capabilities, including a significant increase in max towing capacity with the 2024 models.
Reliability: Generally considered a very reliable engine, with many users expressing satisfaction with its performance and durability.
Common issues: Some reports mention issues like faulty sensors, oil consumption, and spark plug problems, though these are not necessarily widespread.
Older vs. newer models: Vehicles from model year 2020 and 2021 were subject to a safety recall for a potential short circuit, but this issue does not apply to newer models.

Fuel economy

Performance: Fuel economy is comparable to other heavy-duty gas engines, with the highway mileage of 16.2 mpg being the most fuel-efficient highway run seen among tested competitors.
Overall: The final calculated fuel economy was 15.5 mpg, which is on the lower side but within the same ballpark as other heavy-duty gas engines.

What is the life expectancy of a 6L90 transmission?

The life expectancy of a 6L90 transmission varies greatly depending on maintenance, but can reach several hundred thousand miles with proper care, while some can have a shortened lifespan due to inherent problems. Regular maintenance, especially frequent fluid changes (around every 50,000 to 60,000 miles), is crucial for longevity. However, the transmission has known failure points, such as issues with the torque converter, valve body, and solenoids, and some consider it a "ticking time bomb" without modifications.
Factors affecting lifespan

Maintenance: Regular fluid changes are essential to prevent wear and heat buildup. Following the recommended service interval, or even changing fluid more frequently if you tow or drive in extreme conditions, can significantly extend its life.
Known issues: The 6L90 is known to have some inherent flaws, which can lead to failure even with proper maintenance.
Common problems: These include torque converter issues like shuddering, valve body problems, and solenoid malfunctions.
Vehicle use: The lifespan will be affected by how the vehicle is driven. Heavy towing or driving in extreme conditions can shorten the life of the transmission.
Aftermarket upgrades: Some aftermarket upgrades can address the transmission's inherent flaws and improve its durability.

How to maximize lifespan

Change the transmission fluid regularly, approximately every 50,000 to 60,000 miles.
Avoid heavy towing or extreme driving conditions where possible.
Be aware of warning signs of failure, such as slipping, shuddering, or clunking noises, and address them promptly.
Consider aftermarket upgrades if you are experiencing problems or want to proactively increase durability.

What year 2500hd to avoid?

Years to avoid for a 2500HD include 2003–2006 and 2014–2017 due to widespread electrical, transmission, and HVAC issues. For Ram 2500 models, the 2013 and 2018 models should be approached with caution due to engine and braking system problems respectively. More recent Ram trucks, specifically 2021-2023, have also had recalls for potential electrical and fire risks.

Chevrolet Silverado/GMC Sierra 2500HD

2003–2006: Known for a high number of owner complaints and reliability issues, especially with electrical systems, HVAC, and the engine management system.
2014–2017: Models from this period, particularly 2014, 2015, and 2017, had numerous recalls and high complaint rates.
- 2014: Had frequent air conditioning and transmission issues.
- 2015: Had a large number of recalls and is known for suspension and transmission problems.
- 2017: Is frequently cited for significant transmission problems.

Ram 2500

2013: Considered a poor year due to engine problems.
2018: Has the most complaints, with many related to the braking system.
2021–2023: Has a number of recalls and investigations regarding potential electrical shorts and fire risks.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.