Gearing And Tuning Questions

[Josh185]

I have been reading these forums and have learned a lot of great information about my Sierra. I noticed that some of you provide the rear axle gearing in your sigs. How do I find what gearing my 2008 Sierra has? It has the 6.0L in it with 4x4. How do these gears affect the trucks performance?

 

Also, which handheld tuner works best with these trucks? I have had my eye on a diablo trinity because of its features but I wanted to get some opinions from this community.

[Stevens03]

Look at the RPO codes in the glove box.

 

GU6 = 3.42

GT4 = 3.73

GT5 = 4.10

 

If you have the 6-speed, most likely you'll have 3.42's, if you have the 4-speed, then 3.73's are common unless you have the max trailer package (NHT) then that gets you the 4.10's.

 

Post back what you find out.

[MS3DALE]

Look in your glovebox on the SPID label,You'll have either GT4 or GT5....GT4 is 3.73 - GT5 is 4.10 (If you have the NHT pkg. you'll have 4.10)

 

On the tuner....Go with a Black Bear custom tune!

[MS3DALE]

If you have the 6-speed, most likely you'll have 3.42's, if you have the 4-speed, then 3.73's are common unless you have the max trailer package (NHT) then that gets you the 4.10's.

 

He won't have the 6-spd. Steven,It wasn't used on those trucks then.

[Stevens03]

If you have the 6-speed, most likely you'll have 3.42's, if you have the 4-speed, then 3.73's are common unless you have the max trailer package (NHT) then that gets you the 4.10's.

 

He won't have the 6-spd. Steven,It wasn't used on those trucks then.

 

 

Aw... I thought they might of started using the 6-speed in 08...

[Josh185]

Thanks for the quick replies guys. I will take a look in the glove box during my lunch break.

[Josh185]

How do the black bear custom tunes work? I tried reading their FAQ but didnt really help me understand how they tune it. It says an in-person tune is $250 which is what I would like but it doesnt say how they get to me or where I can go to meet them.

[MS3DALE]

If you have the 6-speed, most likely you'll have 3.42's, if you have the 4-speed, then 3.73's are common unless you have the max trailer package (NHT) then that gets you the 4.10's.

 

He won't have the 6-spd. Steven,It wasn't used on those trucks then.

 

 

Aw... I thought they might of started using the 6-speed in 08...

 

 

The HD's and Denali/Escalade's did for '07-'08,The rest didn't start until '09.

[MS3DALE]

How do the black bear custom tunes work? I tried reading their FAQ but didnt really help me understand how they tune it. It says an in-person tune is $250 which is what I would like but it doesnt say how they get to me or where I can go to meet them.

 

For the in-person tune we do "tune meets" and Justin will fly in for them and tune our trucks,Justin is located in San Diego,Ca.

Where are you located?

[Josh185]

How do the black bear custom tunes work? I tried reading their FAQ but didnt really help me understand how they tune it. It says an in-person tune is $250 which is what I would like but it doesnt say how they get to me or where I can go to meet them.

 

For the in-person tune we do "tune meets" and Justin will fly in for them and tune our trucks,Justin is located in San Diego,Ca.

Where are you located?

 

 

I am in Greenville, TX which is about 1 hour northeast of Dallas.

[Josh185]

Ok, I went down to my truck and took a pic of the sticker in the glove box. I am not sure how to tell what I have based on looking at it. I have attached it below so maybe one of you can decode it. Also, would this sticker tell me if it has a locking rear differential?

 

[txab]

GT4 - 3.73

 

G80 - Locker

 

 

http://www.compnine.com/vid.php?vin=2gtek13y481199884

[Z'06]

4th column, third row says GT4, so 3.73 from the factory.

[Josh185]

GT4 - 3.73

 

G80 - Locker

 

Awesome! Thanks for helping me decode that.

 

Now what do the numbers 3.73 translate to in regards to performance? How does having this gearing affect the truck vs one of the other gears?

[Z'06]

Now what do the numbers 3.73 translate to in regards to performance? How does having this gearing affect the truck vs one of the other gears?

 

It all depends on your tire height and mix of city/highway driving. On a 4-speed, it's a great all-around gear on stock ~31" tire height for city performance and highway mileage.