transmission issues 2015 6 speed auto

justinE · June 29, 2020

Ive got a 2015 GMC Sierra, 6 speed trans. 122,000 miles.. for a while I've noticed a shutter like in the trans but always thought it was due to traveling at a low speed and low rpm. when I've noticed this I usually just clicked on the tow mode and it always smoothed out. about a week ago I was traveling around 50-60 mph and I started feeling like a miss or skip. I've had a miss before and an engine light code showed an O2 censor was bad. this time no lights or codes. I assumed maybe it was time for a tune up, I changed plugs and wires, but did not fix the problem. I've read all online about a shutter and skip in the transmissions. I took it to the dealership and had them look it over and theyre saying that its likely a torque converter, but gm recommends a trans swap. any other problems with these and any solutions or other things I can try before I buy a trans?

flyingfool · June 29, 2020

try an ISUZU NPR 4500 with 6 speed trans, get the 6l90E and check the specs on the NPR torgue converter stall speed... call "circle D" trans for more knowlegeable people

shudder is trans pump failure, and TC coming apart.. also get all the updates from "trans go" for the 6l80 or 6l90

Edited June 29, 2020 by flyingfool

carnau · June 29, 2020

8 hours ago, flyingfool said:

try an ISUZU NPR 4500 with 6 speed trans, get the 6l90E and check the specs on the NPR torgue converter stall speed... call "circle D" trans for more knowlegeable people

shudder is trans pump failure, and TC coming apart.. also get all the updates from "trans go" for the 6l80 or 6l90

This is the best advice and the way I would go.

Now, before GM decided to go with "change the whole transmission" for the torque converter shudder. They were having us replace the fluid, if that didn't fix it, replace the torque converter and if that didn't fix it replace the transmission. Just something to think about.

flyingfool · June 29, 2020

I have a 2012 NPR HD. and it regularly pulls 10,000 lbs every day its in use. I never had any strange operations with shift or shudder , its super reliable same trans as a k2 but the 6l90 has some internal upgrades and I think a larger clutch pack piston for better clutch holding power

Edited June 29, 2020 by flyingfool

carnau · June 29, 2020

6 hours ago, flyingfool said:

I have a 2012 NPR HD. and it regularly pulls 10,000 lbs every day its in use. I never had any strange operations with shift or shudder , its super reliable same trans as a k2 but the 6l90 has some internal upgrades and I think a larger clutch pack piston for better clutch holding power

I have this in an 85 K10 that I built. 383 Engine, NPR Trans with a 373 rear end. I Upgraded my TC to the 89-67L though. The only big upgrade I did besides clutches.

LaitModelFan · June 29, 2020

I have the same problem on a 2015 GMC Sierra 1500, 5.3, not sure the model of the 6 speed transmission. 127k miles and it felt like it was missing. I was 400 miles from home and made it home Friday, this morning taking it to my mechanic barely made it 5 miles. He said solenoid was $1200 and probably the torque converter was toast. Going to cost me $3000 +/- to rebuild. I almost traded for 2020 2 months ago, but I love the 2015, its been a keeper until now.

justinE · June 30, 2020

On 6/29/2020 at 6:35 AM, carnau said:

This is the best advice and the way I would go.

Now, before GM decided to go with "change the whole transmission" for the torque converter shudder. They were having us replace the fluid, if that didn't fix it, replace the torque converter and if that didn't fix it replace the transmission. Just something to think about.

Thanks for the advice! I will try this and hope for the best.

flyingfool · June 30, 2020

after checking on my NPR , i notice these trucks do not have the TCC lock up activated in the trans software. most likely NPR doesnt even have torque converter clutches at all.. this is probably why they are more reliable.. only down side of doing this in our trucks is a loss of 2-3 mpg..

Edited June 30, 2020 by flyingfool