6.2 tune out AFM and shiftpoints

Luke Martin · December 3, 2018

All new to the forum, been doing a lot of reading as I'm looking to buy a truck before end of the year. I'm more familiar with LSx based GM engines and pre 2008 stuff. I'm one of the guys that buys stuff keeps it for 10 years and can work on my on equipment for most jobs.

The newer technology has kept me away from newer trucks but with that said, time for a new one now.

I've been looking for 2016 to 2018 6.2s in either Sierra or Silverado. Really like the trucks the only major thing I seem to find is somefolks not as happy with the 8 speed. My buddy has a LTZ 6.2 8 speed and that is his only complaint, just always seems to be in looking for the right gear.

Is anyone running a custom (from a GM speed shop) tuned GM 15+ truck, I'm thinking that with AFM off and maybe some tranny tuning that would be all that's needed to make this a solid combo?

Maybe more common using a Diablo or other hand tunner and turning AFM does this seem to clean up the 8 speed issues I've heard of?

Much appreciated.

1SLOW1500 · December 3, 2018

8 speed sucks. There can be many issues with it. However for the most part you are correct. Tunning can resolve all of it. Personally I would also throw in a new stall but with just light bolt ons and a tune your fine. Get rid of afm/dod and change the torque tables increase shift pressures and zero out slip over set rpm. If mpg aren't the very most important thing for you get into fuel tables and fix the fuel ratio however I would go intake filter, exhaust first.
Any other questions on tune just post or go over to HPT and read up.

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DHeinze · December 3, 2018

I have a 18 Sierra 6.2 8spd Denali Ultimate.

The only complaint I put forward was GMC's choice of putting 3.23 gearing the Denali line. It is the only way to get the 6.2 in 18-19 models that I have seen.

I have put 17,000 on mine pulling a travel trailer at 6,000lbs to truckloads of wet oak firewood.

The fuel milage has been good no real gear seeking except in the mountains which one would expect pulling the travel trailer.

I currently added the diablo I3 to the mix and the extra 20hp and 20 ftlbs of torque with the 93 tune are noticeable. I left the AFM in place and actually have had the truck getting better mileage after the tune. We haven't had a long trip to see the difference at this point.

My intent is to go to 3.73 gearing in the truck in the next month or so because we upgraded the travel trailer and are pulling right at the limit of the truck.

Basically overcoming the flaw GM gave the truck.

Empty on the highway we have seen mpg in the 30's to 40's with a average of 23 to 24 mpg over all.

1SLOW1500 · December 3, 2018

Issue with a gear swap is the truck doesn't know this and the shift tables will leave you in a dead spot at common speed. Need to tune the shifts under demand so the truck doesnt hold gear and not get to overdrive.
My truck does this but I have it set like that so I stay in power band. I can double tap my foot and it will shift. Horrible for mpg and highway but staying in boost and 1200 egt. I can pass every car on the road and be 70-110 in a flash.
I would try bolt ons and a real full custom tune before gears but yes they can make huge difference.

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Grjfer · December 3, 2018

I just switched from a 15 SLT 5.3 6speed to an 18 SLT 6.2 8speed. The 15 had 3.42 gearing and the 18 has 3.23 gearing. I find the 8-speed currently to be much more user-friendly. I hauled a 5x14 trailer load of hickory Sunday and it did great.

Luke Martin · December 3, 2018

Great replies thanks! Gas mileage isn't #1 priority but I do want to get the best possible for what it is. I am in the Atlanta area, I have a job where I am with customers and I also have kids and we do a lot of outdoors, so the truck will get a good 50/50 mix of work driving plus me and kids in the mountains fishing or down at the hunt camp. Truck would be leveled and 4WD

Edited December 3, 2018 by Luke Martin

SILVER SLED · December 3, 2018

1 hour ago, DHeinze said:

I have a 18 Sierra 6.2 8spd Denali Ultimate.

The only complaint I put forward was GMC's choice of putting 3.23 gearing the Denali line. It is the only way to get the 6.2 in 18-19 models that I have seen.

I have put 17,000 on mine pulling a travel trailer at 6,000lbs to truckloads of wet oak firewood.

The fuel milage has been good no real gear seeking except in the mountains which one would expect pulling the travel trailer.

I currently added the diablo I3 to the mix and the extra 20hp and 20 ftlbs of torque with the 93 tune are noticeable. I left the AFM in place and actually have had the truck getting better mileage after the tune. We haven't had a long trip to see the difference at this point.

My intent is to go to 3.73 gearing in the truck in the next month or so because we upgraded the travel trailer and are pulling right at the limit of the truck.

Basically overcoming the flaw GM gave the truck.

Empty on the highway we have seen mpg in the 30's to 40's with a average of 23 to 24 mpg over all.

You could have got 3.42's with the trailering package.

And FYI I love my 8 speed. Shifts awesome. I had a tuned 2015 6 speed 5.3, my current truck is a 6.2 speed unturned, drives awesome.

Edited December 3, 2018 by SILVER SLED

BB68 · December 3, 2018

I hardly feel my 8 speed shifting. Good to me.

DHeinze · December 3, 2018

You could have got 3.42's with the trailering package.

The ultimate package downsized the gearing and it has the trailing package. $17,000 off sticker for the one on the on the lot. $1600 for gearing seemed the better choice than looking elseewhere.

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SILVER SLED · December 3, 2018

3 minutes ago, DHeinze said:

The ultimate package downsized the gearing and it has the trailing package. $17,000 off sticker for the one on the on the lot. $1600 for gearing seemed the better choice than looking elseewhere.

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I'm sorry, I probably should have said the Max Tow package. I think there is a lesser tow package that has limited slip and hitch/wiring stuff... Max tow comes with gear, mirrors and other stuff I can't remember.

DHeinze · December 3, 2018

I'm sorry, I probably should have said the Max Tow package. I think there is a lesser tow package that has limited slip and hitch/wiring stuff... Max tow comes with gear, mirrors and other stuff I can't remember.

Correct. No NHT available for the Denali.

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DHeinze · December 3, 2018

Issue with a gear swap is the truck doesn't know this and the shift tables will leave you in a dead spot at common speed. Need to tune the shifts under demand so the truck doesnt hold gear and not get to overdrive.
My truck does this but I have it set like that so I stay in power band. I can double tap my foot and it will shift. Horrible for mpg and highway but staying in boost and 1200 egt. I can pass every car on the road and be 70-110 in a flash.
I would try bolt ons and a real full custom tune before gears but yes they can make huge difference.

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Keep in mind the '17 and up, 8 speeds are not tunable.

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1SLOW1500 · December 3, 2018

2 minutes ago, DHeinze said:

Keep in mind the '17 and up, 8 speeds are not tunable.

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What are you talking about? They are tuned all the time if you are speaking about how they are locked from the factory HPT has resolved that issue some time ago. In fact you had to send the TCM in and pay to have it unlock but now you just email support. Or am I missing something here?

1SLOW1500 · December 3, 2018

57 minutes ago, BB68 said:

I hardly feel my 8 speed shifting. Good to me.

ask yourself why. then when you find the answer and are pissed off ask how can we fix that and then you will say WOW that's a truck.

DHeinze · December 3, 2018

What are you talking about? They are tuned all the time if you are speaking about how they are locked from the factory HPT has resolved that issue some time ago. In fact you had to send the TCM in and pay to have it unlock but now you just email support. Or am I missing something here?

I just went through it with powerteq. They cannot unlock 17 and up 8 spds. If you have a pre '17 8 speed transmission it is tunable.

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