Tranny Slipping Downhill?

[Bigell]

In my 2020 Yukon SLT w/49K this afternoon, I was driving down a pretty steep hill at around 40MPH. I felt the truck jerk and it dropped gears and speed not once, but twice. I drove maybe another half mile or so but it didn’t happen again. Anyone ever experience this? I paid around 40Grand for this truck and if it’s having tranny issues already it’s going back to Huntington….

 

[Fless]

I was going to say something about the 49 million miles on it, but I won't.

 

[wjburken]

In my 2020 Yukon SLT w/49000K this afternoon, I was driving down a pretty steep hill at around 40MPH. I felt the truck jerk and it dropped gears and speed not once, but twice. I drove maybe another half mile or so but it didn’t happen again. Anyone ever experience this? I paid around 40Grand for this truck and if it’s having tranny issues already it’s going back to Huntington….

Are you sure it wasn’t just down shifting to help maintain speed going down hill? Our 2013 will down shift to let the engine slow the vehicle going down hills.

From your manual.

 

[Bigell]

Are you sure it wasn’t just down shifting to help maintain speed going down hill? Our 2013 will down shift to let the engine slow the vehicle going down hills.

From your manual.

View attachment 403985

I didn’t have the tow/haul mode on at all. I was just driving the same hill I’ve been in in the past. It was weird cuz it jerked and dropped gears twice. Second time I wasn’t even on the hill.

 

[wjburken]

I didn’t have the tow/haul mode on at all. I was just driving the same hill I’ve been in in the past. It was weird cuz it jerked and dropped gears twice. Second time I wasn’t even on the hill.

It may not need tow/haul mode on. Doesn’t in our 2013. If we are trying to slow down fast, but not slam on the brakes fast, it will sometimes downshift sto help slow the vehicle.

My 2016 F-150 does it as well.

 

[Bigell]

I was going to say something about the 49 million miles on it, but I won't.

I fixed it…

 

[NickTransmissions]

In my 2020 Yukon SLT w/49K this afternoon, I was driving down a pretty steep hill at around 40MPH. I felt the truck jerk and it dropped gears and speed not once, but twice. I drove maybe another half mile or so but it didn’t happen again. Anyone ever experience this? I paid around 40Grand for this truck and if it’s having tranny issues already it’s going back to Huntington….

As others have said, it's likely engine braking-driven downshifts which is part and parcel of essentially all transmission shift strategies for later model vehicles as programmed into their respective ecms/tcms.

Keep an eye on it, and let us know if it starts happening on level grades or other symptoms appear (or if your SES light comes on).

Do you have a six-speed?

I believe the 6s were standard and 10-speeds were an option for that year/model/sub-model combo (but could be wrong).

 

[Bigell]

As others have said, it's likely engine braking-driven downshifts which is part and parcel of essentially all transmission shift strategies for later model vehicles as programmed into their respective ecms/tcms.

Keep an eye on it, and let us know if it starts happening on level grades or other symptoms appear (or if your SES light comes on).

Do you have a six-speed?

I believe the 6s were standard and 10-speeds were an option for that year/model/sub-model combo (but could be wrong).

Yes.Definite 6 speed..

 

[NickTransmissions]

Yes.Definite 6 speed..

Visit my 6L80 Info thread if you haven't already as I have consolidated a quite a lot of info on those transmissions. Everything from changes and updates through the years, diagnosis, trouble shooting and rebuild/performance upgrades is incorporated into that thread. There's also quite a few links to TSBs that address common issues/failures folks have experienced with the 6L family of transmissions throughout their production lifecycle.

Let us know if you need more info or start seeing anything else that concerns you. For now, I wouldn't worry too much about it...

 

[CMoore711]

You don’t have to be in tow/haul mode for automatic grade braking to activate.

You can manually select whether you want the automatic grade braking on or off. If you turn it off it won’t ever activate.

I would recommend reviewing your owners manual on the features of your rig; What they do how to turn them off/on or make any adjustments.