2015 GMC Sierra 6 Speed Transmission Problems

Vehicles like the 2015 GMC Sierra 6 Speed are very good for carrying heavy loads and big size tv such as a 65-inch TV from one place to another.

However, for them to function efficiently, they must be maintained regularly. In order for you not to have issues driving this truck, the transmission must be maintained regularly.

2015 GMC Sierra 6 Speed Transmission Problems are:

  • Transmission slipping which can lead to the low and burnt transmission fluid and defective clutch
  • A jerking transmission can lead to a faulty sensor and delayed gear shift
  • Transmission sound problems such as gurgling, whining, and grinding

The GMC Sierra is a widely used vehicle and so its owners have observed and reported some of the transmission issues it has. In this article, we consider the transmission problems of the 2015 GMC Sierra 6 Speed vehicle.

What Transmission Do I Have in my 2015 GMC Sierra?

The 2015 GMC Sierra Hydra-Matic 8L90 has an eight-speed automatic transmission.

Does the 2015 GMC Sierra 6 Speed Have Transmission Problems?

The 2015 GMC Sierra 6 speed has transmission problems. In fact, the car is widely known for many of these transmission problems.

What are the 2015 GMC Sierra 6 Speed Transmission Problems?

The transmission problems affecting the 2015 GMC Sierra 6 Speed are:

1. Transmission Slipping

The transmission in the 2015 GMC Sierra 6 Speed can slip at times. What causes this is when the system does not glide smoothly, during changing of gears.

A loose connection in the bearings of the driveshaft or improper fluid level might also be a cause of slipping transmission and lead to other problems.

Anytime you notice that you have problems shifting the gear of your car, it could be caused by the following:

Low and Burnt Transmission Fluid

If the transmission fluid is not at the appropriate level, the hydraulic pressure is bound to be affected. Lubricants make the gears of a vehicle function smoothly.

In the absence of enough lubricants, the gears might slip and overheat as well. It can also cause the gear to stick in reverse or park, etc.

This happens in extremely hot temperatures of heat and cold – when the car is parked outside during hot weather or snowstorms. If you accelerate and your car shakes, it is a very good indication that the transmission fluid is low.

Even when the car drags while you are accelerating it, it shows that the transmission fluid is low as well. With enough fluid, shifting from gear to gear will be less stressful and heat buildups that affect the gear will reduce.

Defective Clutch

Every driver should know that clutches are an important part of vehicle transmission. The syncing of gears and the managing of power delivery of engines are all carried out by the clutch.

Clutches are more important, why? The converter is integrated with the automatic clutch during high speeds to prevent transmission from slipping.

If the clutch has been damaged or it no longer functions as normal, you should get it fixed as soon as possible – it is a major recipe for disaster while driving that car!! Torque distribution is managed by the clutches.

The clutch is fundamental in car transmissions because it manages the way the gear moves and guarantees the smooth acceleration of the car.

Failed Solenoid

In layman’s terms, the solenoid of a car is the part that is responsible for starting the car between the ignition and the engine.

In the event of a malfunctioning solenoid, excess fluid will be released into the system that is harmful to various components of the car including the seals and clutches.

Worn-out Transmission Gears

Transmission parts need to be maintained properly and regularly to prevent wear-outs. If these parts wear out, you can expect that they will not function in the normal way.

As you accelerate, you will feel a weird jerk in the engine of the car. You should replace the transmission bands often also because they wear out and decrease in quality with time.

The transmission gears can wear out (which is quite normal), which leads to a noticeable rough ride. Check your transmission parts and replace them before it gets too late. Prevention is better than cure!

Torque Converter Problems

A torque converter is a fluid used in a vehicle that transfers rotating power (mechanical energy) from a prime mover to a rotating driven load (in kinetic energy).

It is a very significant component in the transmission of your vehicle. If this important component is damaged or has problems, slipping transmissions can occur which can lead to serious accidents.

2. Jerking Transmission

Drivers of the 2015 GMC Sierra 6 Speed have reported that they sometimes experienced a very rough transmission and rough shifting. A few causes of jerking transmission are listed below:

Low Transmission Fluid

Be careful not to use bad fluid (dark color). The transmission fluid should be clear and light red. Bad fluid means you will find it difficult to change gears.

The lubricating system is the focal point of an automatic gearbox. The wet type and dry type are the main types of lubricating systems.

Faulty Sensor

The sensor sends data to enable transmission. If you have a faulty sensor, it will send the wrong data to the maintenance service of the transmission shifting and you might have problems on the road.

Sensors assist in information flow between computer systems.

A faulty sensor will lead to the distribution of incorrect data from one system to another. This is very dangerous because shifting to the wrong gear can lead to a massive accident. You need to fix this problem as soon as possible if you notice it.

Delayed Gear Shift

It is a major cause of failing transmissions. A delayed response in shifting from one gear to another gear. The delay could last for seconds or minutes and it shows that there are issues with the transmission.

A failed solenoid of inappropriate maintenance of fluid can be a cause for this. There might be other causes though, so it is best to take the car to the experts to check what’s wrong.

3. Transmission Sound Problems

There are so many sounds you will be hearing from your vehicle if the transmission is bad. Sounds like grinding, whining, gurgling, etc. They are really uncomfortable and unpleasant.


Gurgling sounds show there is slipping transmission in 2015 GMC Sierra 6-speed trucks. This could be a result of the bad transmission fluid also.

Transmission fluid does not just act as a lubricant. It cools and shields the internal parts of the system from overheating that will lead to damage.

If you hear a gurgling sound from your engine, it could be a transmission problem, check it ASAP!


While accelerating or just driving, you might hear a whining sound. Oftentimes, it will be high-pitched. It means that there’s a transmission problem and more problems are coming definitely.

To be on the safe side, when you hear a whining sound from your vehicle’s engine, take it to the mechanic and let the problem be discovered.


A grinding sound is definitely a very unpleasant sound. Grinding noise from your engine is a cause for serious concern.

It means some parts of the gear system are loose and are rubbing against each other. It can be caused by other issues which can be found by disassembling some other components of the gear system.

A grinding sound also indicates that there might be other problems with your engine.

What to Do If 2015 GMC Sierra 6 Speed Start Having Transmission Problems?

If your 2015 GMC Sierra 6 starts having transmission problems, do not be so worried. It can be handled.

Actually, there are some DIY steps you can take to solve the transmission issues but if your vehicle still has transmission problems, you will have to take it to the experts to get it fixed.

2015 GMC Sierra 6 Speed Transmission Replacement Cost

Replacing the transmission of the 2015 GMC Sierra 6 Speed is not cheap at all. You may need to spend about $3,000 just to replace the transmission. Many users of the vehicle have complained about the high cost and the durability of the transmission.


The 2015 GMC Sierra 6 Speed has been given bad ratings by some people who were not impressed with the durability of the car.

It is a good vehicle, that’s for sure but people were not happy they had to replace the transmission only a few years after purchasing the car.