Tranny issue? Or electrical issue .

[Conejabelica]

So Rpm’s started going crazy we had it parked for a couple days . Today we tried get it into gm but didn’t make it. You can drive it at a certain rpm but then it will go crazy and like just not go. Can’t be put into reverse when this happens. if you turn off the car and turn it back on it will run but then same thing happens. 
 

2017 gmc sierra single cab . 5.3L 2x4

Edited February 17, 2023 by Conejabelica

[JimCost2014]

Any information about the truck at all would be very helpful, otherwise all you will get are guesses and sarcastic comments.

[asilverblazer]

While you are gathering pertinent information, check engine light ought to be on, so get a code reader and see what codes come up.

[Conejabelica]

20 minutes ago, asilverblazer said:

While you are gathering pertinent information, check engine light ought to be on, so get a code reader and see what codes come up.

No codes on reader. We’ve already done that. No check engine light either 

[asilverblazer]

Does the check engine light function at initial start up? 

On 2/14/2023 at 6:05 PM, Conejabelica said:

Can’t be put into reverse when this happens.

What does this mean? The gear selector cannot be put in the reverse position? If put in the reverse position what does the gear indicator do? Does the lever go into reverse and the indicator indicate reverse but nothing happens?

 

So far I'd expect a torque converter and transmission rebuild is in order. Does the truck otherwise start and run fine? Mileage on the odometer?

 

Any grinding or other odd noises?

Edited February 17, 2023 by asilverblazer

[Conejabelica]

5 hours ago, asilverblazer said:

Does the check engine light function at initial start up? 

What does this mean? The gear selector cannot be put in the reverse position? If put in the reverse position what does the gear indicator do? Does the lever go into reverse and the indicator indicate reverse but nothing happens?

 

So far I'd expect a torque converter and transmission rebuild is in order. Does the truck otherwise start and run fine? Mileage on the odometer?

 

Any grinding or other odd noises?

Correct it will be in the reverse gear . But does not move. weird part is if you turn off the truck and turn it back on you can go in reverse. 
 

the truck runs good . No issues with it till now . It has like 990000

 

its never had any odd noises. It was running good then like one day it just decided to start shifting weirdly. And now this 

[asilverblazer]

The only thing left that might be 'simple' is check all electrical connections to the transmission. If it is not a mechanical failure that requires rebuild it is an electrical issue that a more sophisticated diagnostic tool should uncover.

 

In any case, I would expect a significant number of dash warnings... in other words, if you don't see anything external, its going to need to go to a shop.

[newdude]

On 2/17/2023 at 7:55 PM, Conejabelica said:

Correct it will be in the reverse gear . But does not move. weird part is if you turn off the truck and turn it back on you can go in reverse. 
 

the truck runs good . No issues with it till now . It has like 990000

 

its never had any odd noises. It was running good then like one day it just decided to start shifting weirdly. And now this 

 

 

After you turn it off and turn it on and reverse works, does reverse cut back out again after you start moving?

[Conejabelica]

3 minutes ago, newdude said:

 

 

After you turn it off and turn it on and reverse works, does reverse cut back out again after you start moving?

Yes

[newdude]

57 minutes ago, Conejabelica said:

Yes

 

 

Transmission is highly likely.  We got a 2018 right now doing that.  Converter was smoked which sent debris everywhere and smoked the pump.  It also smoked the 4-5-6 clutch pack and chipped some hard parts somehow.  Curretly getting rebuilt.

 

Time to have the transmission pulled and gone through.