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2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Day to Day Use of Tow/Haul Mode

2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby nvestysly [OP] » Dec 01 2019, 11:01pm

There are several threads on the topic of the 8L90 transmission and its various problems. Our truck is rather jerky (lurching) on upshifts from 1st to 2nd and downshifts from 2nd to 1st. I'm not able to replicate the problem on a consistent basis so it's been difficult to take the service personnel on a test drive and demonstrate the problem. The lurching is probably the same as others have described and our truck may be on the less annoying end of the scale so maybe I shouldn't be complaining.

All our complaints/concerns are at low speed. The worst situation is low speed downshifting and the transmission seems to upshift momentarily and results in a "pushing" sensation and if we're not careful the truck lurches forward. Other than the annoying jerkiness of the upshifts and downshifts, this "pushing" could be considered a safety problem as it could result in a low-speed fender bender.

This has been happening since the vehicle was new. The problem is no worse now at 15,000 miles than it was new. The dealer offered to change/flush the transmission fluid and reprogram the computer. I may take them up on that.

I've recently started driving day to day using tow/haul mode. When I drive in tow/haul the odd shifting goes away entirely. No problem with upshifts or downshifts. Other than the obvious lower MPG is there any reason I shouldn't drive in tow/haul mode every day? Is there any way to set the truck so it's always in tow/haul mode?

I'm also using the plug-in device from Range Technology but that has not made any noticeable difference in my opinion.
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Re: 2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby mjrchabot » Dec 01 2019, 11:43pm

If the dealer is offering a flush, refilling with the new Mobil 1, and reflashing at no cost then do it. Without a question... but yes, it sounds like your truck is just like any other with the 8spd.

Mine has the odd clumsy shift from 1 to 2 and vice versa but nothing too crazy.

Driving around in tow/haul mode won’t harm your truck other than lose MPG.


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Re: 2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby mjrchabot » Dec 01 2019, 11:44pm

Oh, and the Range is really just to disable AFM; won’t change the shift points of your transmission or anything.


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Re: 2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby nvestysly [OP] » Dec 03 2019, 9:01pm

mjrchabot wrote:Oh, and the Range is really just to disable AFM; won’t change the shift points of your transmission or anything.


Some other threads indicated an improvement in shifting with the use of the Range device. I may have read too much into those comments but the people posting thought some of the jerkiness attributed to the transmission may actually originate in the transition from 8-6-4 and vice-versa.

Next time I'm at the dealer I'll take them up on the transmissiion oil change and flashing the chip. I only hope their new "program" doesn't make things worse. Right now it's just a minor annoyance and very easy to get used to.
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Re: 2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby GBSierraSLE » Dec 03 2019, 9:07pm

I supposed a Range could smooth out a downshift since you are not also going from V4 to V8 at the same instant. But that would be the only (indirect) affect it could have on shifting.
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Re: 2018 Sierra, 6.2L, 8-Speed (8L90) Transmission

Postby mjrchabot » Dec 03 2019, 9:14pm

nvestysly wrote:
mjrchabot wrote:Oh, and the Range is really just to disable AFM; won’t change the shift points of your transmission or anything.


Some other threads indicated an improvement in shifting with the use of the Range device. I may have read too much into those comments but the people posting thought some of the jerkiness attributed to the transmission may actually originate in the transition from 8-6-4 and vice-versa.

Next time I'm at the dealer I'll take them up on the transmissiion oil change and flashing the chip. I only hope their new "program" doesn't make things worse. Right now it's just a minor annoyance and very easy to get used to.


As GBSierra mentioned above, any improved driving experience you’ll feel from a Range is just removing the momentary lag you feel from V8 to V4 and vice versa.
Also, just FYI your truck only runs at 8 or 4 cylinders, not 6.


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