Newbie advise appreciated

[Chris41586]

Hi everyone! I found this forum, in hopes that I could get some advise from experienced and knowledgeable people about trucks, performance, ECT... So a few months back, I purchased a 2017 Sierra 1500, with the 6.2 motor. It came with a 6" lift and 35" tires. I love the truck, but noticed immediately, that I'm only averaging about 12mpg. Recently, I came across a guy with basically the same truck, but a Silverado, and he insisted that I need to buy both a superchip F5, as well as a pedal commander, to both help with gas mileage, and says that my transmission will go out if I don't do this, because it's lifted, and it'll keep shifting too low of rpms. Does anyone know if I actually "need" to do this, and how I can tell if it's already been adjusted by the original owner? It seems to be running just fine, but I can't find anything that tells me the correct shifting rpms. I want to give my truck what it needs, but also can't spend a bunch of money on things that aren't necessary at the moment. I would greatly appreciate any advice on that, as well as why my mpg are so damn low. Thanks!

[2018GMC]

Hi everyone! I found this forum, in hopes that I could get some advise from experienced and knowledgeable people about trucks, performance, ECT... So a few months back, I purchased a 2017 Sierra 1500, with the 6.2 motor. It came with a 6" lift and 35" tires. I love the truck, but noticed immediately, that I'm only averaging about 12mpg. Recently, I came across a guy with basically the same truck, but a Silverado, and he insisted that I need to buy both a superchip F5, as well as a pedal commander, to both help with gas mileage, and says that my transmission will go out if I don't do this, because it's lifted, and it'll keep shifting too low of rpms. Does anyone know if I actually "need" to do this, and how I can tell if it's already been adjusted by the original owner? It seems to be running just fine, but I can't find anything that tells me the correct shifting rpms. I want to give my truck what it needs, but also can't spend a bunch of money on things that aren't necessary at the moment. I would greatly appreciate any advice on that, as well as why my mpg are so damn low. Thanks!

The pedal commander and superchip won’t do anything to “save” your transmission. 2017 and 6.2 means you have the 8l90. Besides some clunky shifting now and then it’s a stout transmission.

Monitor your transmission temperature as long as it’s below 240 and running in the range of 180 - 220 that’s the temp GM designed it to operate in.

I’d recommend a AFE sprint booster instead of pedal Commander. All it will do is increase the throttle sensitivity. Pedal commander made in turkey [emoji1250]. AFE sprint booster made in USA [emoji631].

A tuner just increases timing, adds more fuel and may increase pedal sensitivity.

Does your truck have the large camper mirrors? If so it’s max tow package and has 3:42 gear ratio. If f not then 3:23 gear ratio.

12 mpg sounds about right for turning big 35” tires on stock gear ratios.

Welcome to the forum [emoji846]

[2018GMC]

One more thing...

Post some Pics!

[JimCost2014]

Just like 2018GMC said, 12 MPG is not too bad.

 

You have added more weight with the lift, more with the wheels and tires, and have created more resistance when it comes to the rolling mass of the truck.

 

I would take it to a dealership and have them run the VIN for service records, if they are not available (you did not mention current miles), start changing fluids, starting with the transmission, the fluid will tell a good story as to what is happening inside.

Then the rear end, and transfer case. All will show what the lift (if anything) is doing for advanced wear. 

 

You will get many opinions, just like your friend, so the more you can share about the truck the better.

[Chris41586]

1 hour ago, 2018GMC said:

The pedal commander and superchip won’t do anything to “save” your transmission. 2017 and 6.2 means you have the 8l90. Besides some clunky shifting now and then it’s a stout transmission.

Monitor your transmission temperature as long as it’s below 240 and running in the range of 180 - 220 that’s the temp GM designed it to operate in.

I’d recommend a AFE sprint booster instead of pedal Commander. All it will do is increase the throttle sensitivity. Pedal commander made in turkey . AFE sprint booster made in USA .

A tuner just increases timing, adds more fuel and may increase pedal sensitivity.

Does your truck have the large camper mirrors? If so it’s max tow package and has 3:42 gear ratio. If f not then 3:23 gear ratio.

12 mpg sounds about right for turning big 35” tires on stock gear ratios.

Welcome to the forum

So I guess that's what I was confused about, was the gear ratio, and how much it matters if I don't get them changed. I have the regular sized electric mirrors, so I guess not the towing package. I will state that I am a Carpenter by trade, and know very little about mechanics haha. Good advise on the American made parts. I guess I'm comparing other gas trucks with similar upgrades for the mpg, and was hoping I could somehow increase that a little. Apparently the tuner will only adjust the timing for shifting, but the gear ratio is what would really need to be changed? I can for sure try to get ahold of the dealership for records. I bought the truck with right about 11,000 miles on it. I should also mention that I'm new to forums in general, so where do I post pictures? On this thread, or on my profile?

[JimCost2014]

3 hours ago, Chris41586 said:

So I guess that's what I was confused about, was the gear ratio, and how much it matters if I don't get them changed. I have the regular sized electric mirrors, so I guess not the towing package. I will state that I am a Carpenter by trade, and know very little about mechanics haha. Good advise on the American made parts. I guess I'm comparing other gas trucks with similar upgrades for the mpg, and was hoping I could somehow increase that a little. Apparently the tuner will only adjust the timing for shifting, but the gear ratio is what would really need to be changed? I can for sure try to get ahold of the dealership for records. I bought the truck with right about 11,000 miles on it. I should also mention that I'm new to forums in general, so where do I post pictures? On this thread, or on my profile?

Check your RPO sticker in the glove box, look for these codes to see what you have:

G80 Differential, heavy-duty locking rear

GT4 Rear axle, 3.73 ratio

GU4 Rear axle, 3.08 ratio

GU5 Rear axle, 3.23 ratio

GU6 Rear axle, 3.42 ratio

You can post pictures here, "What have you done to K2 today", there is another one for the 14 - 18's, really no rules, post where you like, maybe even a new thread????

Edited May 1, 2020 by JimCost2014

[Chris41586]

13 hours ago, JimCost2014 said:

Check your RPO sticker in the glove box, look for these codes to see what you have:

 

G80 Differential, heavy-duty locking rear

GT4 Rear axle, 3.73 ratio

GU4 Rear axle, 3.08 ratio

GU5 Rear axle, 3.23 ratio

GU6 Rear axle, 3.42 ratio

You can post pictures here, "What have you done to K2 today", there is another one for the 14 - 18's, really no rules, post where you like, maybe even a new thread????

I'm not seeing which ratio it is, but there's a picture of the sticker. Once I figure out this number, what can I do with the info?

[JimCost2014]

22 minutes ago, Chris41586 said:

I'm not seeing which ratio it is, but there's a picture of the sticker. Once I figure out this number, what can I do with the info?

You have the GU5 code, which means the 3.23 rear end, standard with the 6.2 (no Max Tow).

 

You are geared for max fuel economy, with the stock set up. How does the truck feel off of the starting line, does it hold 8th gear on the freeway, or is it hunting between 7 and 8? If it is always trying to find a happy gear, you probably need to go to a 3.73 set up? 

[Chris41586]

1 hour ago, JimCost2014 said:

You have the GU5 code, which means the 3.23 rear end, standard with the 6.2 (no Max Tow).

 

You are geared for max fuel economy, with the stock set up. How does the truck feel off of the starting line, does it hold 8th gear on the freeway, or is it hunting between 7 and 8? If it is always trying to find a happy gear, you probably need to go to a 3.73 set up? 

Off the line, I've always thought it feels pretty good and powerful, although I did buy it already lifted, so I don't have anything to compare it to. I just went on a little drive to test what you're asking: in town, with steady acceleration, shifting around 2,000rpms and holding about 1,100. Depending on how hard I'm accelerating onto the highway, shifting closer around 3,000 rpms and holding about 1,300. It's a little harder to tell what gear I'm in with an 8 speed, because I feel like the shift is so smooth, so I'm not sure if I'm in 7th or 8th, but at 60 mph it does hold steady around 1,200 to 1,300rpms. Not going back and forth. I'll also add that the gauge reads 180 for transmission fluid temp. 

[JimCost2014]

59 minutes ago, Chris41586 said:

Off the line, I've always thought it feels pretty good and powerful, although I did buy it already lifted, so I don't have anything to compare it to. I just went on a little drive to test what you're asking: in town, with steady acceleration, shifting around 2,000rpms and holding about 1,100. Depending on how hard I'm accelerating onto the highway, shifting closer around 3,000 rpms and holding about 1,300. It's a little harder to tell what gear I'm in with an 8 speed, because I feel like the shift is so smooth, so I'm not sure if I'm in 7th or 8th, but at 60 mph it does hold steady around 1,200 to 1,300rpms. Not going back and forth. I'll also add that the gauge reads 180 for transmission fluid temp. 

Kind of sounds like they knew what they were doing. If you are not getting the "flares" of RMP's going up and down, thinking you are ok.

Have you checked to see where your speedometer is? Did they do a relearn, or are you off because of the tire/wheel size?

Edited May 1, 2020 by JimCost2014

[Chris41586]

1 hour ago, JimCost2014 said:

Kind of sounds like they knew what they were doing. If you are not getting the "flares" of RMP's going up and down, thinking you are ok.

Have you checked to see where your speedometer is? Did they do a relearn, or are you off because of the tire/wheel size?

That's good to hear, and I feel a little better having it confirmed that it's performing as normal. As I said before, they may have done some adjustments, but I have no way of knowing without records. Hopefully the dealership will be helpful in that department. The speedo is of around 3mph at 60, but I feel like that's because of the wheel size? The one thing that has concerned me a few times, is the brakes. I've gone to put it in gear a couple of times, and they've felt tight, or almost like a grinding feeling. I thought maybe they needed to be upgraded because of the beefy tires (which I know couldn't hurt), but it's never been a consistent issue, and I just did a VIN search, and saw that there may be a recall for that problem. Have you noticed anything in this manner?

[Chris41586]

1 hour ago, JimCost2014 said:

Kind of sounds like they knew what they were doing. If you are not getting the "flares" of RMP's going up and down, thinking you are ok.

Have you checked to see where your speedometer is? Did they do a relearn, or are you off because of the tire/wheel size?

Also BTW, that's a pretty nice truck you've got yourself as well

[JimCost2014]

59 minutes ago, Chris41586 said:

That's good to hear, and I feel a little better having it confirmed that it's performing as normal. As I said before, they may have done some adjustments, but I have no way of knowing without records. Hopefully the dealership will be helpful in that department. The speedo is of around 3mph at 60, but I feel like that's because of the wheel size? The one thing that has concerned me a few times, is the brakes. I've gone to put it in gear a couple of times, and they've felt tight, or almost like a grinding feeling. I thought maybe they needed to be upgraded because of the beefy tires (which I know couldn't hurt), but it's never been a consistent issue, and I just did a VIN search, and saw that there may be a recall for that problem. Have you noticed anything in this manner?

Check with your dealer to see if you are part of the update for the vacuum pump recall.

 

The 18's have the updated pump, so the brakes are pretty normal (for a 5000+ LB truck). 

 

being a 2017, when does your bumper to bumper expire?

 

And remember, I am by no means an expert, it just sounds like your truck is behaving normal to me.

[JimCost2014]

57 minutes ago, Chris41586 said:

Also BTW, that's a pretty nice truck you've got yourself as well

Thanks, greatly appreciated!!!

[Chris41586]

38 minutes ago, JimCost2014 said:

Check with your dealer to see if you are part of the update for the vacuum pump recall.

 

 

The 18's have the updated pump, so the brakes are pretty normal (for a 5000+ LB truck). 

 

being a 2017, when does your bumper to bumper expire?

 

And remember, I am by no means an expert, it just sounds like your truck is behaving normal to me.

If I remember correctly, the full bumper to bumper expires around October of this year, but I'll have to check the exact date with the dealer. I normally change my own oil, because I don't like paying top prices for full synthetic and I get the specials at AutoZone, but I did go ahead and get the lifetime oil package this time, just because it's an odd number of quarts, and I figured I can justify the $850 it costs for that, although I'm never gonna need 4 changes done in a year. I'll see if I can kill a few birds with one stone here next week, and get the oil, any records they may have, and see if there's any recalls to check out all at the same time. 

 

I didn't expect to find many "experts" here, but it's definitely nice to have input from real world guys that aren't trying to sell me something, and the advice is greatly appreciated.