Two separate trips it stopped shifting

The most common cause of this is low fluid or poor condition. So let's start with checking the fluid level and condition.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Please see the process below and let us know what you find on this.

If the fluid is not the issue then we may want to change the filter if you have not done this in a while. This process is attached below as well.

The fact that this happens so intermittently, it would make sense that it is fluid related so let's start with this and go form there.

Thanks

Okay. Yes, it needs to be hot or the reading will not be accurate. I have found on these trucks that if they are low they do not show it when cold just because the do a pretty good job of draining back to the pan.

So it needs to be hot and running to get an accurate reading. Even if it is not to the full/max line, I would fill it to that line just to be sure that filter is not sucking air. I had a 1998 Dakota with a sister transmission to yours and that is what would happen. The only difference was it was only momentary and then it would bang back into gear. However, it would act like it was in neutral and just rev. Is that what yours does when it stops shifting?

I figured it out because it seemed to do it mostly on hills and fluid is the only thing that knows you on a hill as it rolls to the back of the pan away from the pick up.

Let us know what you find with the fluid and we can go from there but unfortunately at that point, we may have a leak internal to the unit that is bleeding pressure or even a sticking valve in the valve body.

Okay. Any time you are in gear and the RPM just revs, that is because you have a pressure leak inside the unit or there is air instead of oil.

The oil passages inside the unit are sealed passages and they lead to different clutches that need to be applied. The valve body is what changes the direction of this fluid but when there is a leak it is not able to apply the clutch.

Think of a garden hose that has a pretty good size hole in it. The amount of water going into the hose is the same but the amount of pressure at the end is low because you are loosing pressure.

Let us know what happens after the fluid exchange but we may need to try and get a video of this just to be sure we are on the same page because something is telling me I may not be completely understanding what is happening.

Thanks

Okay. That helps. I am curious what happens (if it happens again) after the flush and filter. This sounds like you have metal or debris floating through the system.

Basically when the valves/solenoids in the valve body get stuck then this is the result. When you shut the engine off, the fluid drains back and the debris moves enough for it to operate.

Unfortunately there is not one sign of a transmission starting to fail. One sign is a slipping feeling but also something like what you are seeing. Just ask them to inspect the fluid and pan for metal and clutch debris and see what they find. If this is in there, then the new filter and fluid will extend the life. However, I would start planning on a unit because if I am correct, this issue will get more common until the point when it fails.

Were there any codes? I didn't ask that but normally when this happens it will set a code even if the light doesn't turn on.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Let us know what happens and what they find with the fluid and we can go from there.

Thanks

Okay. That is good. This could be related but this code is not causing the shifting issue. However, if there is a harness issue it could be the same harness for the PCM/TCM causing this issue.

Let us know what they find as I am curious about this.

Thanks