Anyone with a 2015 6.2l with the 8 speed auto?

CRApex · November 22, 2016

My 16 was ok..I just learned to live with some of the quirks..My new 17 is absolutely flawless so far. No shudders, clunks and seems to always find the right gear no problem at all...much smoother than the 16. Fingers crossed it stays this way.

crushNchowda · November 22, 2016

Get in your truck (cold in the morning ) crank it up put it in drive ( not reverse ) first and try to take off and see what happens if I don't wait 5 to 10 seconds after I put it in drive it will slip and not move the engin just revs and this was with the old and new replaced transmission. So let me know what happens

Guess what? My '04 GTO w/ 4 speed auto did this, my G8 GT w/ 6L80E did this, my '07 Silverado w/ 4 speed did this, my '14 sierra w/ 5.3 & 6L80 did this, my 2nd '14 sierra 5.3 w/ 6L8- does this, my friend's '05 LS2 vette w/ 4 speed does this, and my 2015 Sierra 8 speed does this.

Is it ideal? No. But I see a pattern here, GM smallblock V8's mated to GM trannies in RWD platforms seem to have a consistent delayed engagement between the TC & the crank or the yolk & pinion - whatever it is, it aint new, and it aint hard to avoid.

So you KNOW it takes moment to engage on a cold start in the morning? Then WHY would you slam the gas trying to see if you can f**k it up? I also notice it idles higher initially when cold too....you ever think this "problem" may be an inherent design to help "protect" something? Even if it isn't & it is simply a design flaw.....if so many vehicles exhibit it & last 100,000+ miles routinely...maybe its not that bad & you should just get used to it???

I say this b/c as I mentioned above - this tranny behavior is not at all surprising to me as literally EVERY modern RWD, V8, automatic vehicle I've come in contact w/ has done the same thing.

Similar to how every Toyota truck I come in contact w/ rusts from the ground up, how nearly every dodge I've come in contact w/ will have MAJOR mechanical failure at free random (anything from wheel bearings to permanently locked diffs to permanently detached sways that cause "the shake" etc.) - nothing in life is perfect.

silver sled 16 · November 23, 2016

What some people find acceptable others will find completely unacceptable. I have made it a habit of asking anyone I come in contact with that owns a 14 15 16 or 17 sierra or silerado. 6 or 8 speed. 5.3 or 6.2. I get almost the same response. "I love the truck but since you mention it, yeah the transmission is kind of funky". It depends. If you came out of a 1970 pickup you may find these transmissions prefect in every way. If you came out of a fairly new truck you may be unhappy. I myself being a master tech and have owned and driven many new vehicles on regular basis I find these transmissions have excellent potential but programing unacceptable. Nissan, Dodge, ford,Toyota all make multi gear v8 driven transmissions. They all shift well imo. The aftermarket tune guys get the 6 and 8 speed gm to shift perfectly. I can't understand why gm has somewhat given up on these units and gone to 10 speed. I'm sure blackbear doesn't have access to the kind of infastructure that gm has when it comes to designing tunes but somehow they get it done and make a lot of people happy.

GullLakeMi · November 23, 2016

What some people find acceptable others will find completely unacceptable. I have made it a habit of asking anyone I come in contact with that owns a 14 15 16 or 17 sierra or silerado. 6 or 8 speed. 5.3 or 6.2. I get almost the same response. "I love the truck but since you mention it, yeah the transmission is kind of funky". It depends. If you came out of a 1970 pickup you may find these transmissions prefect in every way. If you came out of a fairly new truck you may be unhappy. I myself being a master tech and have owned and driven many new vehicles on regular basis I find these transmissions have excellent potential but programing unacceptable. Nissan, Dodge, ford,Toyota all make multi gear v8 driven transmissions. They all shift well imo. The aftermarket tune guys get the 6 and 8 speed gm to shift perfectly. I can't understand why gm has somewhat given up on these units and gone to 10 speed. I'm sure blackbear doesn't have access to the kind of infastructure that gm has when it comes to designing tunes but somehow they get it done and make a lot of people happy

Good post. I agree. I drove a Audi Q7 diesel for 3 years prior to my Sierra Denali. The 8 speed in that was amazing! Smooth, always in right gear. NEVER a single clunk. I also tow a 5k trailer infrequently. Q7 is great and we've kept it as my wife's DD. Now with the Sierra 8 speed I get a clunk and funny shifts on every trip. Funny thing is, my wife doesn't like big vehicles and she agrees the Sierra rides smoother than the Q7 from a suspension and steering standpoint. Why can't they get the transmission right after making cars for 100+ years?????

wayles · November 23, 2016

What some people find acceptable others will find completely unacceptable. I have made it a habit of asking anyone I come in contact with that owns a 14 15 16 or 17 sierra or silerado. 6 or 8 speed. 5.3 or 6.2. I get almost the same response. "I love the truck but since you mention it, yeah the transmission is kind of funky". It depends. If you came out of a 1970 pickup you may find these transmissions prefect in every way. If you came out of a fairly new truck you may be unhappy. I myself being a master tech and have owned and driven many new vehicles on regular basis I find these transmissions have excellent potential but programing unacceptable. Nissan, Dodge, ford,Toyota all make multi gear v8 driven transmissions. They all shift well imo. The aftermarket tune guys get the 6 and 8 speed gm to shift perfectly. I can't understand why gm has somewhat given up on these units and gone to 10 speed. I'm sure blackbear doesn't have access to the kind of infastructure that gm has when it comes to designing tunes but somehow they get it done and make a lot of people happy.

You hit it right on the head there. I find it amazing and frustrating that GM seems to have given up on this and just moved on. The transmission is the ONLY thing I don't like about my truck.

It's also frustrating that there are so many "fixes" out there, all of which never work for everyone. Turn off grade braking, new torque converter, drive in tow/haul mode, etc. Other than a new torque converter, I've tried them all. They seem to work for a while, then the transmission seems to learn it's way back to bad shifting. I have to constantly change up my routine. Oddly, the only thing that helps consistently (but does not solve the issues) is when I mat the peddle up to 70 or so a couple of times. After that, the shifts aren't as rushed and seem a little smoother. Not a very practical solution, but a fun one none the less.

My wife has had a '14 and now a '15 Grand Cherokee with the 8 speed and it shifts perfectly. Come on GM. Get your act together!

GMC-AT · November 23, 2016

Most of the awful trans driveability issues have to do with MPG savings. GM could care less... as long as they can squeak out a little more MPG by doing this plus countless other things. If they can claim 1 extra MPG over Ford, it will help them sell thousands of extra trucks each year. You guys have to remember, a lot of buyers could care less about brand, they just look at MPG.

Personally MPG is near the bottom on my list.. but I'm not the majority. It is what it is...

Docknow9 · January 20, 2017

I have a 2015 GMC Sierra Crew Cab SLT w/6.2 8 spd. It has 29,000 miles and I have averaged 20 mpg for those miles. It is a wonderful truck except for the vibrations I started experiencing two months ago. At first I thought wheel bearing and it went away, then it did it at 70 miles per hour, then thirty miles per hour, today at fifty five on cruise control. I use cruise control almost 90 Percent of the time. It is due for servicing in a couple of weeks and I am going to push the dealer on the transmission. They have always worked with me before, so i will see how good they really are after reading all of these posts. I have had many GM products, 2 Chevy, 3 Fords, 13 Pontiacs, 6 GMC's. This Sierra up until now is the BEST driving and handling vehicle I have owed, and trouble free.