New GM 8spd tranny

cw41

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#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

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#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

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#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

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#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

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#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

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#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