How to tell which transmission you have?

99Mastercraft · April 15, 2018

Good evening guys,

I recently purchased a 2017 GMC Sierra SLT - All terrain. I thought for sure it was a 6 speed, but tonight I put it in low and on the gear shifter it has the option to go all the way up to 8.... I am assuming that is because it’s the 8 speed?

How can I tell which transmission I have?

I REALLY hope it’s not the 8 speed, due to all the issues they have and I don’t have much warranty left.

Any help is appreciated.

qwank · April 15, 2018

that's how you tell, you have an 8 speed

99Mastercraft · April 15, 2018

7 minutes ago, qwank said:

that's how you tell, you have an 8 speed

I figured so.. 12k miles left on warranty, should I have the dealer check it out? I have searched for TSB's and haven't been able to find anything specific. I always end up on a website that doesn't work..

SirenRed16 · April 15, 2018

Good evening guys,

I recently purchased a 2017 GMC Sierra SLT - All terrain. I thought for sure it was a 6 speed, but tonight I put it in low and on the gear shifter it has the option to go all the way up to 8.... I am assuming that is because it’s the 8 speed?

How can I tell which transmission I have?

I REALLY hope it’s not the 8 speed, due to all the issues they have and I don’t have much warranty left.

Any help is appreciated.

You have the 8 speed. How much miles does it have for you have to have little warranty left?

Sent from my SAMSUNG-SM-N920A using Tapatalk

99Mastercraft · April 15, 2018

Just now, SirenRed16 said:

You have the 8 speed. How much miles does it have for you have to have little warranty left?

Sent from my SAMSUNG-SM-N920A using Tapatalk

47k miles. one owner

reardiff · April 15, 2018

There's a few different ways to tell, but if it shows 8 when in manual selection then you have the 8 speed. Another more definitive way to find out is to check the RPO codes on the sticker on the inside of the upper glove box. MYC = 6 speed and M5U = 8 speed. Easiest way to verify would be to drive at a nice and even acceleration up to highway speed and count how may times it shifts. Also all 6.2's come with the 8 speed. In addition, you can ask your local dealer to provide you a build sheet that will show all options your truck with built with. This would be a nice way to see anything else you thought you had and didn't or didn't know you had.

For what it's worth I have a 2017 that bought new last year and have had zero problems with the 8 speed. There's some on this forum who do, and I feel for them based off the stories they have to tell, but don't let that get in your head thinking you have a lemon. Just drive it normal, enjoy the new ride and have any problems fixed or at least documented before your warranty expires. Certainly not worth loosing any sleep over.

TJay74 · April 15, 2018

All 6.2 trucks from 2015 on got the A8, in 2016 all 6.2 trucks and any 5.3 truck with the LTZ/SLT package got the A8.

mjm-1957 · April 15, 2018

If it has a transmission dipstick its a 6 speed. The 8 speed has a fill plug on the case and no dipstick.

HoosierZ · April 15, 2018

3 hours ago, TJay74 said:

All 6.2 trucks from 2015 on got the A8, in 2016 all 6.2 trucks and any 5.3 truck with the LTZ/SLT package got the A8.

My 2016 LTZ has the 5.3 w/ 6 spd. I believe the 8 spd was a late ‘16 or ‘17 change.

Donstar · April 15, 2018

You can find earlier threads complaining about the 6 spd. and then the 8 spd became the target. Complaints are usually legit to the particular owners'vehicle, but issues become highly concentrated on a forum. You will find many will speak highly of their transmission choice in threads that aren't focused on a transmission problem. Enjoy your truck and this forum. Most GM truck owners are very proud of and happy with their vehicles. I know I am.

Donstar · April 15, 2018

Also, you should ask at your local GM dealership for a build sheet for your truck. You may also ask for a list of RPO codes if they aren't listed in your glove box. These will tell you all the specific features of your new truck!

99Mastercraft · April 15, 2018

Thanks guys.. as of right now the only thing I am experiencing is when the vehicle is cold you put it in drive and it seems like when you first start there’s a slight hesitation and a clunk, but goes away after driving and does not exist when it’s warm... I could live with it, but I might see if there’s a software update for the trans before warranty expires

2017_whitez71 · April 16, 2018

If you put it in manual shift mode and it goes to L8 it's an 8 speed.

99Mastercraft · April 16, 2018

Thanks for the replies guys. I stopped by my dealer and expressed concerns about the TSB’s and the clunk you get when it’s cold....

They wanted to keep the truck to take the pan off and perform a flush or multiple flushes and update the software, etc.

They put me in a 2018 Silverado Crew cab 5.3L with 6 speed trans and I definitely like my truck better... also I like the 8 speed better than the 6 speed