2019 Silverado 2500 High Country Tranny Issue

[2019 Red]

I have a 2019 Silverado 2500 High Country that we mainly use to pull our 9000-pound travel trailer. 

It does a wonderful job doing towing and we love the truck. It has just over 65500 miles on it.

It had 6.0 Duramax diesel with the Allison transmission.

over the last month on three occasions, while not towing, when we made a stop, it has seemed the

transmission did not disengage. 

 I had to almost stand on the brakes to stop but the rear wheels kept slowly turning. The first time,

when I released the brakes, the truck lunged forward. the other two times I have shifted to neutral

to release the transmission.

 My truck has been parked for a month waiting to get into the GMC service department where we

bought it February, 2022.

[Bikerjon]

6 hours ago, 2019 Red said:

I have a 2019 Silverado 2500 High Country that we mainly use to pull our 9000-pound travel trailer. 

It does a wonderful job doing towing and we love the truck. It has just over 65500 miles on it.

It had 6.0 Duramax diesel with the Allison transmission.

over the last month on three occasions, while not towing, when we made a stop, it has seemed the

transmission did not disengage. 

 I had to almost stand on the brakes to stop but the rear wheels kept slowly turning. The first time,

when I released the brakes, the truck lunged forward. the other two times I have shifted to neutral

to release the transmission.

 My truck has been parked for a month waiting to get into the GMC service department where we

bought it February, 2022.

Sorry wrong forum. You need the HD forum. This is for T1 1500s. Our trucks don't use Allison transmissions.

[redwngr]

Fwiw, the duramax in a 2500 is a 6.6L

In a 2019 it's the L5P version. 

 

You'll definitely get more reads and responses in the HD area 

 

[Konstantin Vass]

1. Transmission Fluid: Low or contaminated fluid can cause shifting issues. Since the truck is at the dealership, they should check the fluid levels and condition.

2. Torque Converter Problems: If the torque converter isn't disengaging properly, it can lead to the behavior you're describing. 

3. Transmission Control Module (TCM): A malfunctioning TCM may not be sending the right signals for the transmission to disengage.

4. Brake Issues: Sometimes, brake components can fail or stick, leading to the sensation that the transmission isn’t disengaging. Make sure they check the brake system thoroughly.

5. Mechanical Issues: Internal transmission problems, like stuck valves or solenoid issues, could also be at play.

[2019 Red]

On 9/18/2024 at 10:53 PM, Konstantin Vass said:

1. Transmission Fluid: Low or contaminated fluid can cause shifting issues. Since the truck is at the dealership, they should check the fluid levels and condition.

2. Torque Converter Problems: If the torque converter isn't disengaging properly, it can lead to the behavior you're describing. 

3. Transmission Control Module (TCM): A malfunctioning TCM may not be sending the right signals for the transmission to disengage.

4. Brake Issues: Sometimes, brake components can fail or stick, leading to the sensation that the transmission isn’t disengaging. Make sure they check the brake system thoroughly.

5. Mechanical Issues: Internal transmission problems, like stuck valves or solenoid issues, could also be at play.

Thanks for your response, we finally have truck in for service, now we wait. I honestly know nothing about transmissions but I believe everything you mentioned could be possible except #4. The last episode happened in loose gravel and it was 

definitely throwing rocks with both feet on the brake pedal.