Update: Last night I checked the trans fluid level, it was correct and the fluid is nice and clean. I also took a quick look at the wiring as some people with other transmission/ transfer case issues had problems with wiring rubbing and damaging the wires. Nothing obvious, but could certainly have missed something in the dark. There are an awful lot of exposed connections and places where the harness is routed tight to moving/ vibrating parts. Side note, the dealer spent months diagnosing an emissions problem when this truck was new and eventually repaired or replaced a lot of the exhaust harness, so a wiring issue wouldn't surprise me at all. I also tried pulling the transfer case fuse as someone had said they had an issue with wiring and the transfer case would try to shift on its own, that did not help in my case.

It seems to be getting worse. When I left for work this morning I was able to pull out of my driveway fine, but as soon as I stopped at the first light it slipped out of gear and took a few seconds to catch. I circled around the block to head home, and in that 1/2 mile it happened several more times. It now will pop in and out of gear several times when I'm trying to get moving, does not sound good and cant be good for the truck. I drove it to the shop and this happened several times on the way, a couple times I wasn't sure if I would be able to get going. Once its moving everything is normal, shifts and drives fine, only time I have a problem is when I stop.

It seems like an electrical/ electronic issue to me, but also seems like it could be tough to diagnose/ trace, so if anybody else has any more info/ suggestions that would be great.

 

Interesting Youtube 6L50 build

 

This morning I had a very strange thing happen several times on the way to work. I pulled out of my driveway and went a few hundred feet and stopped at the light down the street. When the light turned green I let my foot off the brake and nothing happened, I pressed the accelerator and it just revved up like it was in neutral. I tried going neutral back to drive and still nothing for a few seconds, then it eventually went into gear hard and lurched forward.

I pulled over, peeked under the hood (not much to see) and looked under the truck for dripping fluid. I tried in and out of gear start stops several times in the parking lot and everything seemed to work fine. I continued my ride to work which is about 25 miles of highway and side roads. For the most part everything seemed fine, truck shifted normally, no noise or vibration on the highway. When I got closer to work it did the same thing a few more times. It was always from a complete stop, would not move, motor would rev freely and then eventually start moving, sometimes pretty harshly.

Truck is a 2017 Canyon Duramax, ~65k. Transmission fluid was drained and filled twice (to get most of the old fluid out) and a new filter last summer at around 55k.

I have only found one other post describing this type of behavior. His transmission was fixed or replaced under warranty which unfortunately I am just outside. Has anyone had this happen? Any ideas on what I should check?

Update: Last night I checked the trans fluid level, it was correct and the fluid is nice and clean. I also took a quick look at the wiring as some people with other transmission/ transfer case issues had problems with wiring rubbing and damaging the wires. Nothing obvious, but could certainly have missed something in the dark. There are an awful lot of exposed connections and places where the harness is routed tight to moving/ vibrating parts. Side note, the dealer spent months diagnosing an emissions problem when this truck was new and eventually repaired or replaced a lot of the exhaust harness, so a wiring issue wouldn't surprise me at all. I also tried pulling the transfer case fuse as someone had said they had an issue with wiring and the transfer case would try to shift on its own, that did not help in my case.

It seems to be getting worse. When I left for work this morning I was able to pull out of my driveway fine, but as soon as I stopped at the first light it slipped out of gear and took a few seconds to catch. I circled around the block to head home, and in that 1/2 mile it happened several more times. It now will pop in and out of gear several times when I'm trying to get moving, does not sound good and cant be good for the truck. I drove it to the shop and this happened several times on the way, a couple times I wasn't sure if I would be able to get going. Once its moving everything is normal, shifts and drives fine, only time I have a problem is when I stop.

It seems like an electrical/ electronic issue to me, but also seems like it could be tough to diagnose/ trace, so if anybody else has any more info/ suggestions that would be great.

I am having a very similar issue with my transmission. It FEELS like the fluid is low, but I have been given a lot of possible culprits as to what is wrong with it.

The transmission shop I am going to for diagnosis has been around for 50 years; I am fairly confident they are not going to screw me over, (unlike the dealer!). They are going to check for low fluid levels, TCM codes that may have been thrown, and will take it for a test drive. Here is the link to the thread I started...

I AM HAVING PROBLEMS WITH THE 6L50 SIX SPEED AUTOMATIC...

I am having a problem with the Hydra-Matic 6L50 six-speed automatic transmission in my 2017 Chevrolet Colorado with the Baby Duramax engine. The problem started to occur occasionally and now is increasing in frequency. I am wondering if other Colorado and Canyon diesel owners are experiencing...

www.coloradodiesel.org

 

I am having a very similar issue with my transmission. It FEELS like the fluid is low, but I have been given a lot of possible culprits as to what is wrong with it.

The transmission shop I am going to for diagnosis has been around for 50 years; I am fairly confident they are not going to screw me over, (unlike the dealer!). They are going to check for low fluid levels, TCM codes that may have been thrown, and will take it for a test drive. Here is the link to the thread I started...

I AM HAVING PROBLEMS WITH THE 6L50 SIX SPEED AUTOMATIC...

I am having a problem with the Hydra-Matic 6L50 six-speed automatic transmission in my 2017 Chevrolet Colorado with the Baby Duramax engine. The problem started to occur occasionally and now is increasing in frequency. I am wondering if other Colorado and Canyon diesel owners are experiencing...

www.coloradodiesel.org

Thanks for reply. After doing what I could myself (checking fluid level and looking for obvious electrical/ connector issues) I brought it to my mechanic. They checked a few more things and talked to their transmission shop who said they think its a valve body problem. The truck has been at the transmission shop for a week, hoping for an update today.

 

I’m having the same issue truck been in shop 2 weeks warranty says I need to provide reciept of service who keeps those trying to find the owner of shop but I think he died and they closed down