2016 GMC Sierra 1500 Transmission & Axle Gear Ratios

Whether you are looking to maximize your towing capacity or squeeze every last drop of fuel efficiency out of your daily commute, understanding the powertrain specifications of your 2016 GMC Sierra 1500 is vital. This truck was offered with robust engine choices and a couple of distinct transmission options, coupled with varying rear differential ratios to suit different needs.

Below is a comprehensive guide to the transmission and axle gear ratios for the 2016 GMC Sierra 1500.

Transmission gear ratios

For the 2016 model year, the GMC Sierra 1500 came equipped with either the proven Hydra-Matic 6L80 6-speed automatic transmission or the more advanced Hydra-Matic 8L90 8-speed automatic transmission. The 8-speed was standard on the 6.2L V8 models and available on higher trims with the 5.3L V8.

6-Speed Automatic (6L80)

8-Speed Automatic (8L90)

Available axle ratios

GMC offered several axle ratios for the 2016 Sierra 1500 to accommodate different lifestyles, ranging from highway cruisers to heavy-duty haulers.

How to identify your axle ratio

Identifying the exact axle ratio of your 2016 GMC Sierra 1500 is very straightforward thanks to General Motors' Service Parts Identification (SPID) label.

1. Locate the RPO Sticker: Open your glove box (in some trims) or check the passenger side door jamb. Look for a silver or white sticker loaded with three-digit alphanumeric codes. These are your Regular Production Option (RPO) codes.
2. Find the G-Code: Scan the alphabetical list for a code starting with "G".
   • GU4: 3.08 ratio
   • GU5: 3.23 ratio
   • GU6: 3.42 ratio
   • GT4: 3.73 ratio
3. Check for G80: While you are looking, see if your truck has the G80 code. This indicates the presence of the Eaton heavy-duty automatic locking rear differential (often called a "Gov-Loc"), which provides immense traction benefits.
4. VIN Decoder: Alternatively, you can run your truck's Vehicle Identification Number (VIN) through a GM VIN decoder online or at your local dealership's parts department to get a full build sheet.

Towing vs MPG impact

The relationship between your rear axle ratio and your truck's performance is a balancing act between low-end torque and high-speed efficiency.

• Numerically Lower Ratios (e.g., 3.08): A "taller" gear ratio means the driveshaft turns fewer times to rotate the wheels once. This results in lower engine RPMs at highway speeds, significantly improving fuel economy (MPG). However, it sacrifices off-the-line grunt and reduces overall towing capacity.
• Numerically Higher Ratios (e.g., 3.42, 3.73): A "shorter" gear ratio requires the driveshaft to spin more times per wheel rotation. This multiplies engine torque, making it much easier to get a heavy trailer moving and reducing transmission hunting on hills. The trade-off is higher engine RPMs at cruising speeds, which negatively impacts fuel economy.

Common issues

While the differentials in the 2016 GMC Sierra 1500 are generally robust (utilizing the reliable GM 8.6-inch or 9.5/9.76-inch axles depending on engine and tow package), they are not immune to wear and tear over time.

• Ring & Pinion Whine: If you hear a whining noise that changes pitch depending on whether you are accelerating or decelerating, it often points to worn ring and pinion gears or improper backlash.
• Carrier Bearing Wear: A low-pitched rumble at speeds above 20 mph can indicate worn carrier bearings.
• Limited-Slip / Locker Issues: For trucks equipped with the G80 automatic locking differential, harsh engagements or a failure to lock under wheel slip can occur at higher mileages. This is typically due to governor mechanism wear or clutch pack degradation resulting from a lack of fluid maintenance.

If you are experiencing drivetrain noises or want to re-gear your truck for better towing performance, you shouldn't tackle this precision job alone. Find a driveline shop on Repairius.