New GM 8spd tranny

cw41

Hero Member
Joined
Nov 21, 2006
Messages
533
Likes
6
Points
18
Location
Arizona
#1
Make
GMC
Model
Sierra 1500
Year
2018
Miles
7500
Engine
5.3 hybrid gas/elec
Has anyone had issues with GM's new 8spd tranny? This is the sloppiest shifting tranny from gm yet that I've owned, especially in the 5-15mph traffic it feels like its dropping into neutral and back to 1st or 2nd gear. Launch back and forth in and out of gear it feels like. Its not the auto-stop that I'm having issues with. While at stop sign/light, at times it feels like you have been bumped in the rear?? tach either shows autostop or idle. Didnt notice this issue when new, now just 7,500 miles 6 month old truck.
Went to gmc dealer to see and tech rode with me and noticed my concerns but no codes or updates that he could find and had no experience with my complaints. Sent me on my merry way.
I think gm has 18 tsb's on the 6 and 8 spd issues.
So, I called gmc cust assistance and see what they can do for me.
Thanks for any tips as to other gm/gmc owners that have problems with the new 8 spd. I hear that the 2020's will have a new 10 spd?? More confusion.
thanks
 

cw41

Hero Member
Joined
Nov 21, 2006
Messages
533
Likes
6
Points
18
Location
Arizona
#3
thanks bp!! I saw a tsb that they found the current tranny fluid was retaining moisture and now flushing with mobil 1 synthetic lv atf fluid part #19417577. tsb is 18-na-355
 

cw41

Hero Member
Joined
Nov 21, 2006
Messages
533
Likes
6
Points
18
Location
Arizona
#4
2018 gmc 1500 8spd now is showing code P0711. Having troubles finding out exactly what this entails? Its at the shop under warranty and appears that there is a short or something in the harness to tranny or in tranny?? thanks bp if you are there.
 

bp042665

hunting nut
Joined
Nov 26, 2012
Messages
639
Likes
16
Points
18
Location
Iva South Carolina
#5
DTC P0711
Transmission Fluid Temperature Sensor Performance
The transmission fluid temperature sensor is located inside of the Transmission Control Module assembly which has no serviceable parts. The transmission fluid temperature sensor provides transmission fluid temperature information to the Transmission Control Module. This fault is handled inside the Transmission Control Module and no external circuits are involved.
 

cw41

Hero Member
Joined
Nov 21, 2006
Messages
533
Likes
6
Points
18
Location
Arizona
#6
thanks bp, the tech disconnected something from the drivers firewall under the hood and had leads from it going to to underneath to the tranny. This code showed after a flush with gm's new latest and greatest fluid that is not supposed to attact moisture, so they say. Very poor shifting around town and three service visits later, then they flush and pickup the code on test drive?? Do they drop the pan to replace this sensor? thanks bp!!
 

cw41

Hero Member
Joined
Nov 21, 2006
Messages
533
Likes
6
Points
18
Location
Arizona
#8
they replaced the tcm on the firewall driver side and relearn the tranny and it seems to be ok for now. I'm told the relearn takes 100+ miles to learn my habits?? trans control module about 130.00 part and flush with the new fluid. Couldnt get them to change the filter without me paying for it. we'll see its under the 5yr-60k powertrain warranty. I wonder if gm will offer an extended powertrain warranty for me?? I think i will ask. thanks for your input bp!
chuck
 
Joined
Aug 28, 2007
Messages
4,791
Likes
26
Points
48
#9
Our 2015 Elantra is six speed, remember the Chevy Power Glide with two speeds? Called those turtle torque.

Driving in town can drive you nuts in drive, constantly shifting gears even up to 5th gear at 25 mph and the engine is lugging at this speed. But can shift to the left and leave it in manual mode, finding getting far better fuel economy driving in 2nd or 3rd.

Wife wanted a stick, been driving these all of her life, but if you buy a stick can't get cruise control. But showed her how to work in manual mode and just make believe you are stepping on the clutch. One kid has Chrysler products with AT's, they are the same. He has the same problem in drive, constantly switching gears in town. Suggested manual mode

With a manual can drop it into first gear at 90 mph and release the clutch, and blow the engine, can't do this with the auto in manual mode, can shift but won't drop until you are under the red line speed.

Think these young engineers are smoking crack designing transmissions this way and you sure don't get better fuel economy driving in 8th gear at 20 mpg, engine is lugging like crazy.

We use manual mode a lot, especially for slowing down saving cooking your brakes.

Ha, my bicycle has 27 gears, at my age, 1st is enough for me, but it doesn't have an R.