2018 Sierra, 6-speed or 8-speed trans? And other gripes.

SouthpawHD · July 10, 2018

So I recently purchased (2 weeks ago, but literally just picked up yesterday) a 2018 Sierra SLT Premium and I was under the impression that the 8-speed was standard on all SLTs. Is that not the case? Did I want the 8-speed over the 6-speed trans? It has the 6-speed, just wondering what it maybe should have had vs my expectations.

Also, truck was to come with rear sliding window, per the dealer's description. It did not. Disappointed.

Also thought it was to have rear and front parking sensors. It does not. Disappointed.

Waiting for the dealer to get back to me about adding a rear slider, so we'll see. There was no way to completely verify everything since the truck was in transit. I am already having some slight regrets about buying this truck and trading my 2500 Silvy. It's a great truck, lots of features, and looks amazing, but just wondering what the SLT Premium gave me over just getting another Silvy LT+.

diyer2 · July 10, 2018

I don't buy new but I would never have driven it off the lot if it wasn't what I wanted or was told it was equipped with.

SouthpawHD · July 10, 2018

28 minutes ago, diyer2 said:

I don't buy new but I would never have driven it off the lot if it wasn't what I wanted or was told it was equipped with.

I was trying not to do that, but unfortunately it didn't work out perfectly. Don't get me wrong, its a REALLY nice truck, just not EXACTLY what I had wanted.

newdude · July 10, 2018

Not trying to come off as a smart arse, but did you look the truck over before purchasing to notice it didn't have features you wanted in it? I wonder if the truck was either built during a possible constraint, or the dealer pulled a fast one on you and obviously stated it had features it didn't really have. You wouldn't happen to have the VIN handy? I wonder what the build really shows for options on it.

JamesAT18 · July 10, 2018

Check the window sticker, it should state what all options came with your truck. I'd try to work it out with the dealer to get the options you're lacking.

But there is SLT and then SLT Premium packages.... You probably ended up with just a SLT. Premium packages come with all things you stated you're lacking

Check out the different names of each here:

https://www.gmc.com/trucks/sierra-1500-pickup-truck/build-and-price/packages

Best of luck,

James

mookdoc6 · July 10, 2018

I believe it's one of those GM package deals.....Premium Plus...gets you the LED's, sprayed in bed liner, running boards, rear slider window, parking assist front,back.

The actual M5U is added option or 8speed. I would not get all worked up over the 8speed/6peed. If your pulling things all the time on hills the 8speed will be where it's at...if your driving in town the 6speed is where it's at.......MPG's nadda difference you or I would be able to tell

mjm-1957 · July 10, 2018

Your much better off without the 8 speed, nothing but a headache.I am the transmission guy at a GMC Buick dealer and the M5U leaves alot to be desired.....

damnthetorpedoes · July 10, 2018

42 minutes ago, mookdoc6 said:

I believe it's one of those GM package deals.....Premium Plus...gets you the LED's, sprayed in bed liner, running boards, rear slider window, parking assist front,back.

The actual M5U is added option or 8speed. I would not get all worked up over the 8speed/6peed. If your pulling things all the time on hills the 8speed will be where it's at...if your driving in town the 6speed is where it's at.......MPG's nadda difference you or I would be able to tell

This^

The premium plus package adds everything you are bummed out about, including the 8 speed.

mookdoc6 · July 10, 2018

36 minutes ago, mjm-1957 said:

Your much better off without the 8 speed, nothing but a headache.I am the transmission guy at a GMC Buick dealer and the M5U leaves alot to be desired.....

What is the issue than with the 8speed other than GM'S programming? Failure rate? GM....programs firmer shifts on cold fluid to warm it up....It clunks for 5K up to 10K before it figures it all out? I have not clunked in 50K? Please explain all the Problems with this Tranny....Thanks!

BCMoto · July 10, 2018

I was going to get a sierra but it didnt have the 8spd it had the 6spd and it was alright but i ended up with silverado with the 6.2 and the 8 speed and it drive better i think.

mjm-1957 I would like to know why i made the mistake of getting the 8spd

mjm-1957 · July 10, 2018

That transmission has been a problem since it was released in 2014. The first ones were built with too much clearance between the steel clutch plates and the case. The clunking and noises they made were unbelievable. Unfixable also, we were checking the build dates and the Julian dates on the trans themselves and relaying that off to GM and they would then send a complete replacement.Then the shifting problems started,delayed engagement into reverse after sitting overnight, delayed engagement into drive anytime, harsh 3-2 or 2-1 downshift that felt like you got rearended.We were updating the updates, performing fast learn adapts etc etc etc.Then the TCC shudder started showing up,are you kidding me? First we were told to drop the pan ,replace the filter and blow out the cooler lines and run it for ten minutes on the lift, drop the pan again, drive it on the lift for another ten minutes and another drop of the pan and maybe it will get better after it is driven 200 miles.All of this is done while burning your arm on the cat because they couldn't even put a ****ing dipstick on that piece of shit.I almost forgot the countless valve body replacements to try and correct some shift quality concerns. The six speeds have been virtually trouble free compared to the eight speeds.

NWI Denali · July 10, 2018

Did you sign off on the truck without looking it over?

newdude · July 10, 2018

1 hour ago, mookdoc6 said:

What is the issue than with the 8speed other than GM'S programming? Failure rate? GM....programs firmer shifts on cold fluid to warm it up....It clunks for 5K up to 10K before it figures it all out? I have not clunked in 50K? Please explain all the Problems with this Tranny....Thanks!

The only really big deal seems to be the fishbite/chugging resulting in a triple fluid flush, and if it comes back, replacement of the torque converter. Goes away after that. 8L45 and 8L90 both have the same deal. We've done maybe 6-8 torque converters here at work so far. No valve bodies, etc. Have yet to see one torn apart.

adamj2121 · July 10, 2018

I have a 6 speed and the shifting is terrible. I drove an 8 speed for about a week and it shifted much smoother and seemed to have better programming than my 6 speed. It seems to me you can get a crappy 6 speed or a crappy 8 speed. You also have a chance of getting a good 6 speed or a good 8 speed. It seems to be a matter of luck to me.

Brandon5799 · July 10, 2018

I think you either got a good 8 spd or not. My dads is night and day different compared to mine. His only down shifts hard for first a few minutes while mine has about all the symptoms others have had. Downshifts that feel like the u joints could rip apart, had the tc flushed for shudder, mine sometimes acts like it doesn’t fully engage in park if I’m on a hill as it pops 2 or 3 times with any weight on it before it locks the wheels. Most annoying one is when I’m in 1st gear in a parking lot and let off the gas before it shifts to 2nd it will slam itself in 2nd while I’m coasting and it’s loud enough I flinch every time.