GM's latest service bulletin provides additional details about the next-generation 2027 Chevrolet Silverado 1500 and GMC Sierra 1500, including a larger diesel exhaust fluid tank, transmission cooling changes, and revisions to the transfer case and suspension systems.

General Motors released bulletin # 26-NA-284 on October 21, 2026, outlining the features and mechanical changes introduced with its next-generation light-duty pickups. While several specifications were already known, the document provides some additional information about the 3.0L Duramax diesel and other components shared across the truck lineup.

For Duramax owners, one of the most notable confirmations is an increase in diesel exhaust fluid (DEF) capacity. GM has also provided more information about the optional 34-gallon fuel tank and its estimated driving range.

2027 Duramax DEF Tank Capacity Increases to 7.4 Gallons

The 2027 Silverado 1500 and Sierra 1500 equipped with the 3.0L LZ0 Duramax will receive a larger DEF tank.

According to GM, capacity increases from 20.5 liters to 28 liters, representing an increase of approximately two gallons. The previous tank held approximately 5.4 gallons, while the new capacity is approximately 7.4 gallons.

GM describes this as a 40% increase in capacity, although the exact difference between the published figures is approximately 36.6%.

The additional capacity should allow owners to travel farther between DEF refills, particularly during normal highway driving. DEF consumption can increase considerably while towing, making the additional capacity useful for owners who regularly pull trailers.

The bulletin does not explain whether GM redesigned the physical tank, modified its usable capacity, or changed the surrounding components to accommodate the increase.

It also does not identify whether the revised tank can be installed on earlier LZ0-equipped trucks.

Optional 34-Gallon Diesel Fuel Tank Offers Up to 900 Miles of Range

GM also confirms the availability of an optional 34-gallon fuel tank, identified by RPO NLA.

When paired with the 3.0L Duramax in a properly equipped truck, GM estimates that the larger fuel tank can provide up to 900 miles of highway driving range.

The 34-gallon tank had previously appeared in 2027 vehicle information, but the new bulletin specifically identifies the estimated highway range.

Reaching 900 miles on 34 gallons would require an average of approximately 26.5 mpg. That figure is consistent with the type of highway fuel economy the 3.0L Duramax can achieve under favorable conditions, although actual results depend on vehicle configuration, driving speed, terrain, and load.

The larger fuel tank and increased DEF capacity address two separate operating-range limitations. The fuel tank extends the distance between diesel refueling stops, while the larger DEF tank reduces how frequently owners need to replenish exhaust fluid.

Four Engines, All Paired With the 10L80 Transmission

The 2027 next-generation Silverado and Sierra lineup includes four engine options, all paired with the 10L80 10-speed automatic transmission.

The Duramax retains its previously announced output of 305 horsepower and 495 lb-ft of torque.

Although the bulletin confirms the 10L80 designation for all four engines, it does not provide detailed information about internal transmission revisions, torque converters, or calibration differences between the applications.

Transmission Cooling System Changes

GM describes a revised transmission cooling arrangement for trucks equipped with the new sixth-generation V8 engines.

The new design uses a stack-plate transmission oil cooler mounted beneath the bellhousing area, replacing the transmission oil cooler previously incorporated into the radiator side tank.

Coolant is routed through an auxiliary coolant control valve and into the stack-plate cooler. Short transmission fluid lines connect the cooler to the transmission.

This arrangement changes the location of the transmission's heat exchanger and the way coolant is routed through the cooling system.

The bulletin specifically identifies the changes for V8-equipped trucks. It does not establish that the LZ0 Duramax uses the same arrangement.

Transfer Case Oil Pump and Suspension Changes

Another mechanical update involves the transfer case.

GM identifies an improved oil pump and pickup tube design inside the transfer case, although the bulletin does not provide further information about the revisions or identify the individual transfer case applications.

The rear suspension also receives several configurations depending on vehicle equipment and RPO codes. These include a new steel single-leaf spring with a helper spring, a composite single-leaf spring, and a traditional steel multi-leaf spring design.

Off-road suspension changes include additional jounce control dampers for the ZRX suspension package. GM also identifies 34-inch tires for trucks equipped with the Z7X two-inch lift suspension and 35-inch tires for the ZRX off-road suspension.

The bulletin does not establish which of these configurations are offered with the Duramax.

Updated Trailering Features and Towing Ratings

Maximum towing capacity for the next-generation Silverado 1500 increases to 13,700 pounds, while the Sierra 1500 is rated for up to 13,500 pounds when properly equipped.

These figures represent maximum ratings for the respective truck lineups and should not be interpreted as the towing capacity of every engine or trim combination.

GM has also revised the Trailering App to display vehicle towing and loading weight information.

Another change involves Reverse Automatic Braking when a trailer is connected.

Trucks equipped with a Trailer Interface Module can use that module to determine whether a trailer is attached and disable Reverse Automatic Braking accordingly. Vehicles can also detect trailers using rear radar sensors, although this method may require some forward movement before a trailer is recognized.

Drivers can additionally disable Reverse Automatic Braking through the vehicle settings or controls displayed when shifting into Reverse.

Additional Technology and Interior Updates

The new trucks introduce several electronic and interior features, including a redesigned infotainment interface, updated driver displays, and additional camera systems.

GM lists a standard 16.3-inch infotainment display and a standard 12.2-inch driver information display. Available equipment includes an 11.5-inch front passenger display, a 15-inch head-up display, and an 8.5-inch rear camera mirror.

Apple CarPlay and Android Auto are included in the bulletin's description of the new user interface, alongside Google built-in and the Google Gemini assistant.

Available underbody cameras provide front and rear views for off-road driving and include washer systems for cleaning the camera lenses.

The side-view camera arrangement has also changed. Cameras are mounted in the fixed mirror bases rather than the folding mirror heads, allowing the camera view to remain stationary when the mirrors are folded.

GM has also introduced available digital key and NFC key card functionality. The bulletin notes that digital key hardware will be installed on appropriately equipped trucks, but full activation of the digital key feature is scheduled for a later date.

What Remains Unknown About the 2027 LZ0 Duramax

Although the new bulletin contains useful information about the 2027 trucks, it does not provide additional technical details about several previously identified LZ0 engine updates.

Those include changes to the pistons, turbocharger vanes, NOx sensor, engine sealing, and injector corrosion protection.

The bulletin also does not specify whether the increased DEF tank capacity applies to every Duramax trim and configuration or whether the revised components can be retrofitted to earlier trucks.

For now, the confirmed diesel-specific developments are the 28-liter DEF tank, the available 34-gallon fuel tank with its estimated 900-mile highway range, and continued use of the 305-horsepower, 495-lb-ft LZ0 Duramax with the 10L80 transmission.

Source: General Motors Service Bulletin # 26-NA-284, 2027 Next-Generation Chevrolet Silverado 1500 and GMC Sierra 1500 Light-Duty Trucks New Model Features, released October 21, 2026.