2018 8L90 Delayed shifting

[Travis Crawford]

Bought this truck last year, noticed differences in shifting compared to previous silverados I have owned, some subtle, some not so subtle.

• Accelerate to 35mph, let off the gas coming up to a stop sign, the truck's remains in gear and sounds like an engine brake as approaching the stop sign.  I previously recall my trucks RPMs dropping to 800-1000 when I'd let off the gas and coast, like going into neutral.
• Sometimes when setting cruise to 60mph, my truck will remain at 2K+ RPM for extended period of time before finally shifting to the 1.5K range.
• When towing these issues are amplified.  Interstate driving at 69mph.  My truck runs 2.2K rpms.  If I decrease my setpoint a few mph the truck will shift into a higher gear and RPMs drop to 1.7K. Going up a hill, it jumps to 3.3K-4.5K depending on how long the hill is.  Sometimes it hangs at that high rpm after i've gone over the hill and back down it for a period of time. I often try to tap the break, reduce my cruise set points, trying to get it to shift into the next gear.

 

I've taken the truck to 2 difference shops, and they've tried diagnosing and found nothing.

 

Do I just pull with it and if it blows it blows or what? lol

 

Has anyone else experienced this and found a solution to make it better, or is this just the nature of this POS 8 speed?

 

Thanks for your help.

[newdude]

I'd have the fluid changed and try and have a service shift adapt learn done.  Dealer or perhaps a shop can pull up service bulletin 16-NA-019 and follow the steps in it.  It might help at higher mileage but its possible some of what you are experiencing can return.  

 

Make sure its the fluid GM calls for, p/n 19417577 which is Mobil 1 Synthetic LV ATF HP (blue label on the bottle).  

 

Otherwise, early 8 speeds can have some oddities with shifting but otherwise tend to hold up compared to the 6L80 of the same year window (2015-2018).

Edited July 1, 2025 by newdude