2015 GMC Sierra 2500 HD 6L80 - Transmission Not Shifting and Hihg RPMs

joanie carter · October 23, 2023

I have a 2015 GMC Sierra 2500 HD 6L80 approaching 50K miles. I purchased it back in 2020 with only 19K miles. It started not wanting to shift into 3rd a few weeks ago and coded P0700. We changed the transmission fluid and filter. The fluid was dark 'dirty' red and there wasn't any metal in the pan. We hoped that fixed the issue; took it for a test drive and the same thing happened about 20 mins into the drive. Reset the computer system and still having the issue. It codes sometimes and will give an additional code of P0741. We clear the computer and drive, it will not act up until around 170 degrees temp for the trans fluid or if the cruise control wants to stay in a gear and the RPMs go over 3K.

Now today, it drove fine to work (20 miles) but on the way home, the radio panel started changing channels and then within 5 minutes, the transmission went back to it's old ways of not wanting to change gears. It will change and it doesn't smoothly but the RPMs are around 2000-2200 when going around 55 mph. No clue if this is related BUT about a month before the trans acting up, it was doing this randomly then stopped.

For the 30K miles that I've had the truck, it's been mainly for hauling my horse, horse trailer and back/forth to the barn. The longest haul distance has been about 3 hours away then back. The short distances are under 30 mins away/back.

I don't want to get screwed over by the dealership. I've heard many have had issues with their 2015s around 50K miles for their transmission. I haven't been driving it much as I have a back up car. I would greatly appreciate any advice, etc. Thanks so much.

newdude · October 23, 2023

1 hour ago, joanie carter said:

I have a 2015 GMC Sierra 2500 HD 6L80 approaching 50K miles. I purchased it back in 2020 with only 19K miles. It started not wanting to shift into 3rd a few weeks ago and coded P0700. We changed the transmission fluid and filter. The fluid was dark 'dirty' red and there wasn't any metal in the pan. We hoped that fixed the issue; took it for a test drive and the same thing happened about 20 mins into the drive. Reset the computer system and still having the issue. It codes sometimes and will give an additional code of P0741. We clear the computer and drive, it will not act up until around 170 degrees temp for the trans fluid or if the cruise control wants to stay in a gear and the RPMs go over 3K.

Now today, it drove fine to work (20 miles) but on the way home, the radio panel started changing channels and then within 5 minutes, the transmission went back to it's old ways of not wanting to change gears. It will change and it doesn't smoothly but the RPMs are around 2000-2200 when going around 55 mph. No clue if this is related BUT about a month before the trans acting up, it was doing this randomly then stopped.

For the 30K miles that I've had the truck, it's been mainly for hauling my horse, horse trailer and back/forth to the barn. The longest haul distance has been about 3 hours away then back. The short distances are under 30 mins away/back.

I don't want to get screwed over by the dealership. I've heard many have had issues with their 2015s around 50K miles for their transmission. I haven't been driving it much as I have a back up car. I would greatly appreciate any advice, etc. Thanks so much.

Needs a torque converter at a minimum. The code showing up P0741 is a good sign that hopefully nothing else isn't damaged internal to the transmission other than the converter failed. They should drop the transmission and pull the front cover off and inspect the pump for wear. If they see wear, they should tear it down further and inspect all the other components internal.

Edited October 23, 2023 by newdude