2011 Sierra Denali Transmission Slip

[Ben W]

Hi All,

 

My first post, so I hope I'm posting in the right section. I checked a few other threads here on tranny slip issues, but none seem to line up with my issue.

 

I recently purchased a 2011 Sierra Denali 6 speed with 79k. When driving around normally (revs under 2,500-3k), the transmission seems to shift perfectly smooth up and down. But when I get on the gas heavy, I'm noticing some slip (engine revs to about 5k before the lower gear will engage). Eventually the gear does grab, but then it will peg off redline when it should upshift also. I checked the ATF and it was low, so I did a full flush and filter. The fluid still seemed fairly clean and unburnt. I am not getting any engine codes, my trans temp always seems normal, and there are no visible leaks anywhere (at least what my untrained eye could spot) at the lines up front or the pan. After the flush, it did seem to improve somewhat, but it still exhibits the same behavior when I really get on the gas. Has anyone else experienced this, and if so, what was your findings? Any feedback is appreciated, as I am trying to get to the bottom of this before my 60 day warranty expires.  

 

Thanks in advance!

 

-Ben

[mymaggiebell]

I have a 2010 and my truck would do it while it was still under warranty, in both stock and tuned. Doesn’t throw a code, but mine slips under regular throttle and the RPMs will just jump. I change fluid every 40000kms and never any issue with findings. Also does it so intermittently that there is no rhyme or reason why.

Edited April 30, 2021 by mymaggiebell

[Ben W]

Thanks for the input @mymaggiebell. I might try an additive next, as it is the only other "non-invasive" thing I can think to try at the moment. Its a shame to have these kind of issues right out of the gate, especially with only 80k on the clock. I'll report my findings if the additive works.

[CamGTP]

You could take it back to where you bought it and drive it with a mechanic in the truck. If they see what you are seeing then it should be something they need to fix.

[Dwayne78]

On 4/30/2021 at 11:45 AM, Ben W said:

Hi All,

 

My first post, so I hope I'm posting in the right section. I checked a few other threads here on tranny slip issues, but none seem to line up with my issue.

 

I recently purchased a 2011 Sierra Denali 6 speed with 79k. When driving around normally (revs under 2,500-3k), the transmission seems to shift perfectly smooth up and down. But when I get on the gas heavy, I'm noticing some slip (engine revs to about 5k before the lower gear will engage). Eventually the gear does grab, but then it will peg off redline when it should upshift also. I checked the ATF and it was low, so I did a full flush and filter. The fluid still seemed fairly clean and unburnt. I am not getting any engine codes, my trans temp always seems normal, and there are no visible leaks anywhere (at least what my untrained eye could spot) at the lines up front or the pan. After the flush, it did seem to improve somewhat, but it still exhibits the same behavior when I really get on the gas. Has anyone else experienced this, and if so, what was your findings? Any feedback is appreciated, as I am trying to get to the bottom of this before my 60 day warranty expires.  

 

Thanks in advance!

 

-Ben

My 2011 GMC SIERRA DENALI  has the 6.2 and my transmission got to the point it was doing the exact thing I took mine to BIG DAWGS TRANSMISSIONS and my clutches and some valve bodies were sticking. Fixed it in 1 day had it back 24 hours later $1100 it helps when you know the owner and you do a lot of welding and fabrication for them as well. There is also a valve body on that transmission you can tighten or loosen the control how smooth she shifts or how fast and hard you want it to shift as well, all depends on the way you turn it and how you like it. I do a lot of pulling so mine shifts fast and hard with a built transmission and new hardened gears I'm ready to pull the world on faster circles

[Dwayne78]

6 minutes ago, Dwayne78 said:

My 2011 GMC SIERRA DENALI  has the 6.2 and my transmission got to the point it was doing the exact thing I took mine to BIG DAWGS TRANSMISSIONS and my clutches and some valve bodies were sticking. Fixed it in 1 day had it back 24 hours later $1100 it helps when you know the owner and you do a lot of welding and fabrication for them as well. There is also a valve body on that transmission you can tighten or loosen the control how smooth she shifts or how fast and hard you want it to shift as well, all depends on the way you turn it and how you like it. I do a lot of pulling so mine shifts fast and hard with a built transmission and new hardened gears I'm ready to pull the world on faster circles

 

[Dwayne78]

On 4/30/2021 at 5:10 PM, Ben W said:

Thanks for the input @mymaggiebell. I might try an additive next, as it is the only other "non-invasive" thing I can think to try at the moment. Its a shame to have these kind of issues right out of the gate, especially with only 80k on the clock. I'll report my findings if the additive works.

 

Just now, Dwayne78 said:

 

I would definitely take the pan off the transmission,  a lot of times these part time mechanics will leave the old "O RING" or seal in the transmission because sometimes they don't come out with the screen and stay in so when they put the new screen in it doesn't create a air tight seal so it sucks air and fluid does not get where it needs to go. I would check that first of all. And Lucas transmission stabilizer helped a few of my transmissions . Hope this helps.