GMC Sierra is quite a reliable truck. It offers five capable power trains, including a fuel-efficient diesel, and respectable towing and hauling capacities for the class. The Sierra is quiet and comfortable, with a cushioned ride and spacious seats. The interior looks good, and there are plenty of intuitive tech features.

The GMC Sierra 1500 was equipped with the 4L60E in early models and 6-speed 6L80 in later models, and 8-speed 8L90 in 2015+ models. The GMC Sierra 2500 HD came equipped with the 4L60E transmission, 4L65E transmission, and 4L80E transmission in early models. Later models got the 6L90 6-speed transmission, and the GMC Sierra 2500HD 6.6L Duramax Diesel had the Allison 1000 transmission.

The GMC Sierra 3500 HD was GMC’s answer to the heavy-duty pickups from Ford, Dodge, and Chevrolet. Early versions were equipped with the 4L80E transmission and the 6L90 6-speed in later models. The GMC Sierra 3500HD 6.6L Duramax Diesel got the Allison 1000 transmission.

It is so significant to know what to look for when you want to purchase anything. Here we have elaborated on different problems transmissions might have, their costs, and fluids so that you could make an informed decision. You can also read about other common issues with the 1500 here.

What Transmission has the GMC Sierra Used?

Here is a list of transmissions used by different models of GMC Sierra:

GMC Sierra 1500

• 4L60E Transmission
• 4L65E Transmission
• 4L80E Transmission
• 6L80 Transmission
• 8L90 Transmission (2015+)

GMC Sierra 2500

• 4L60E Transmission
• 4L65E Transmission
• 4L80E Transmission
• 6L90 Transmission
• Allison 1000 Transmission

GMC Sierra 3500

• 4L80E Transmission
• Allison 1000 Transmission (6.6L and 8.1L Diesel Only)
• 6L90 Transmission

How Long Does a GMC Sierra Transmission Last?

With good maintenance, a GMC Sierra can reach 150,000 miles, with many models reaching 200,000 miles. Surveys have shown that about 1.7% of the GMC Sierras on the road today will surpass the 200,000-mile marker.

GMC Sierra 1500

With good maintenance, a GMC Sierra can reach 150,000 miles, with many models reaching 200,000 miles. Surveys have shown that about 1.7% of the GMC Sierras on the road today will surpass the 200,000-mile marker.

GMC Sierra 2500

On average, the GMC Sierra 2500 HD transmission lasts for between 130,000-180,000 miles.

GMC Sierra 3500

On average, we’ve seen the GMC Sierra 3500 HD transmission last for between 130,000-180,000 miles.

How Much Does a GMC Sierra Transmission Cost?

Sometimes it becomes hard to decide if you want to buy a transmission just because you are not familiar with the price. Most commonly, transmission costs range from 2500$-3000$. Here we have mentioned estimated prices for your GMC Sierra transmissions:

• 4L60-E transmissions costs around $1,795
• 4L80-E transmissions costs around $2,031
•  6L80 transmissions costs around $3,899
• 4L65E transmissions costs around $1,799
• 6L90 transmissions costs around $3,899
• 8L90 transmissions costs around $5,894
• Allison 1000 costs around $3000

How Reliable Is The Transmission On A GMC Sierra?

The GMC Sierra’s transmission reliability varies per year and model. Older models (1999-2007) with the 4L60-E showed more issues. Later models (2007-2013) with the 6L80/90 fared better, and recent models (2014-onwards) with 6, 8, and 10-speed transmissions show improved reliability. Diesel variants with Allison transmissions are notably robust.

If we go back in time, GMC Sierras that were produced between 1999 to 2007, which mainly feature the 4-speed 4L60-E automatic transmission, have been known to present certain reliability issues.

Common problems have included shifting inconsistencies, slippage, and eventual transmission failure, particularly in higher-mileage vehicles. Considering that the Sierra can hold up into the 200,000 mile range, it’s not uncommon to see higher-mileage models on the road.

In contrast, the later models from 2007 to 2013, equipped with the newer 6-speed 6L80 and 6L90 automatic transmissions, have a better track record. These units seem to have fewer issues, although they are not without their own set of potential problems.

Overheating can be an issue with these transmissions, particularly if the vehicle is regularly used for towing or other heavy-duty applications- especially if you’re not fueling up the right way.

From 2014 onwards, GMC Sierra has used 6-speed, 8-speed (8L90), and 10-speed (10L80 and 10L90) transmissions, depending on the model and engine option. By and large, these transmissions are known for their durability and smooth operation.

The 8-speed transmission, in particular, had some teething issues with rough shifting and torque converter problems. Many of these concerns were addressed by the time the 10-speed transmission rolled out, providing better shift quality and performance and I rarely see big issues with the 10-speed the way I do with the earlier transmissions.

I’ve also seen, and heard from other folks, that the Diesel variants are a lot more solid and reliable compared to their gasoline counterparts which is consistent with most Diesel models. That’s another plus for the Sierra that some other GMC models, like the Arcadia, don’t offer.

Common GMC Sierra Transmission Problems

Let us discuss the problems regarding transmissions of GMC Sierra 1500/2500/3500.

4L60-E

4L60-E might cause the following problems and you’ll see many of these issues in similarly sized trucks that share the same transmission like the Chevy Silverado or the GMC Yukon among others.

• Problems with shifting into 3rd gear whereas the car acts like it’s in neutral. The problem here is 3/4th gear clutch pack failure. You’ll need new pistons and a clutch pack to replace this.
• You lost your second or reverse gear. In this case, we’re talking about a broken drive shell that will need to be replaced.
• Problems with shifting into 2nd gear with a possible ‘check-engine light. The problem here is a worn TCC regulator valve that causes the converter clutch to slip.

4L65E

Following are some of the problems one might face with 4L65E transmission.

• One may experience an unusually harsh 1-2 shift
• Loss of reverse, second and fourth gears. The first and third gears will seem to function normally.
• No movement when the transmission is shifted into Drive or the 3rd gear position. It is possible to experience normal operation when the transmission shifted into second, first, or reverse.
• The vehicle might be stuck in third gear, the instrument cluster may not function

4L80E

The 4L80-E is not a transmission with many problems. However, there are some things that you should look out for. The 4L80E transmission could bring the following issues.

• One might experience irregular shifting-sometimes a throttle position sensor or input/output speed sensor fails on the transmission which causes it to develop erratic shifting.
• Overheating is another symptom that can sometimes occur (especially when towing heavy loads). The only thing you can do here is to make sure that there’s enough transmission fluid in the transmission. Otherwise, damage may occur to the clutches, seals, and valve body.

6L80

Vehicles with 6L80 might face the following issues.

• No forward or reverse engagement or slipping between the gears.
• Vehicles may slip when Reverse is selected or have no/delayed reverse engagement, harsh shifts from 2-3 / 4-5 or slips while in fifth, and slipping acceleration when passing.

8L90

8L90 transmissions issues might include:

• Excessively hard or abrupt gear changes.
• One may experience harsh shifts, delayed shifts, unexpected downshift, stuck in a gear, and/or hesitation to shift.
• Drivers may experience a pronounced delay in forward or reverse gear engagement after shifting from Park. This condition typically occurs when the vehicle has been sitting for several hours with the engine off (like overnight).

6L90

Vehicles with 6L90 might face the following issues.

• No forward or reverse engagement or slipping between the gears.
• Vehicles may slip when Reverse is selected or have no/delayed reverse engagement, harsh shifts from 2-3 / 4-5 or slips while in fifth, and slipping acceleration when passing.

Allison 1000

• Trucks equipped with the Allison 1000 6-speed automatic transmission may have been built with an incorrect transmission thrust bearing. Over time, this bearing could fail, resulting in noise and poor transmission operation.
• Drivers may experience intermittent no forward or reverse the condition, the possibility of a flashing PRNDL display, or a range shift inhibited message in the driver information center with no saved DTCs.
• GMC Sierra 3500HD trucks equipped with the Allison 1000 6-speed automatic transmission, may have a condition in which increased transmission oil cooling circuit pressure may cause transmission fluid to weep or leak. This loss of fluid occurs near the transmission cooler at the crimp joints on the metal ends of the cooler line where it joins the rubber hose. The increased oil cooling circuit pressure typically occurs while driving in extremely low temperatures.

Difference between Transmissions

The 4L60E is an electronically controlled 4-speed automatic transmission and It weighs 133 pounds without transmission fluid.

The 4L65E is a 4-speed electronically controlled transmission and it weighs 194.6 pounds.

The 4L80E transmission is a 4-speed automatic gearbox that uses similar architecture as the venerable TH400. It weighs around 254 pounds without transmission fluid.

The 6L80 and 6L90 are 6-speed electronically controlled transmissions. The only difference between them is the strength of internal components. Its dry weight is 195 lbs.

8L90 is a General – 8-speed automatic with a traditional torque converter. It weighs 210+ lbs.

Allison 1000 5-speed transmissions, and some are even six-speed and can handle up to 620 pound-feet of torque.

Transmission Fluids and the GMC Sierra

Transmission fluid plays a significant part in keeping your car running steadily and smoothly. One must monitor fluid type and its level regularly.

The main reason behind observing the car fluid is to ensure that the fluid level is correct. Without it, your car transmission will break down in no time. Keep in mind, that a loud transmission isn’t the only sign of a problem and a vehicle that’s running quieter than usual could be related to a lack of transmission fluid too.

It is essential to change the transmission fluid of the GMC Sierra every 45000 miles or so to keep your car on the road.

• 4L60-E / 4L80-E/6L80 is compatible with Dexron VI
• 4L65E is compatible with Dexron 3
• 6L90 is compatible with DEXRON VI
• 8L90 is compatible with Dex 6 HP Transmission fluid
• Allison 1000 is compatible with Dexron vi

Sources

• https://transmissionrepairguide.com
• https://my.gmc.com/content/dam/gmownercenter/gmna/dynamic/manuals/2016/GMC/Sierra/2016%20GMC%20Sierra%201500.pdf