Rear axle, 3.08 vs. 3.42 Explaining the difference

Chris · October 18, 2013

I was into it hard. Probably lag from the TM

jay15892 · October 18, 2013

Yea the throttle has to be pushed in more then my 2011 or 2013 did. Once I had about 1000 miles on mine the engine seemed to loosen up and now it feels way faster then it did. Im about halfway thru my first 89 octane (I usually use 87) tank full of gas and the engine definitely seems to run smoother. Gas milage seems about the same though. I think you probably need at least 5000 to 8000 miles and a oil change for these engines to truly be 'broken in". At least that was how my 2011 was. Didn't keep my 2013 long enough to confirm that. lol..

2014 Sporty Shorty · October 18, 2013

The stock tuning on these trucks is fairly conservative, I have been paying close attention to the timing/rpm of my truck and even though running the 94 auto bumped it up a bit and gave more power, there is still quite a bit left on the table. Once I figure how the cam likes to make power I will tinker a bit more with the intune. I don't see why you couldn't get yourself 30 whp with just an intake and tune with some good gas or E85. Don't forget that when your using DI, you will always get more power because you can run leaner and have a much more stable afrs which gives me the confidence to run more timing. The transmission is actually set up pretty stiff from the factory and seems to shift way faster than the previous gens with the 6L in stock form.

crushNchowda · October 18, 2013

Also - not many people have put a ton of miles on yet. My first 2014 w/ the 3.08's got peppier after I had put about 4,000 miles on it - the tranny adapts and the motor gets broken in. I can imagine seeing just shy of 400HP and north of 400 lb/ft w/ only an intake and tune on these DI 5.3's

For comparison sake - my initial tune on a bone stock G8 GT w/ the 6.0 that had AFM and obviously not direct injected netted 28whp - that's HUGE.

Dialing down the torque mgmt or removing it all together if you're feeling frisky will really wake these things up as well.

MikeNH · October 18, 2013

Also - not many people have put a ton of miles on yet. My first 2014 w/ the 3.08's got peppier after I had put about 4,000 miles on it - the tranny adapts and the motor gets broken in. I can imagine seeing just shy of 400HP and north of 400 lb/ft w/ only an intake and tune on these DI 5.3's

For comparison sake - my initial tune on a bone stock G8 GT w/ the 6.0 that had AFM and obviously not direct injected netted 28whp - that's HUGE.

Dialing down the torque mgmt or removing it all together if you're feeling frisky will really wake these things up as well.

E85 will get you 385/400+ on a stock 5.3 in the 2014s.

clayp · October 18, 2013

Someone here compared the old 3.73 with a 4 spd auto to the new 3.42 with the 6spd auto. The 6 speed I guess has lower gear ratios and a wider spread. My 01 with 3.73 and a cammed 6.0 doesn't feel much quicker than the new 6spd/5.3/3.42 combo

KMGMC · October 18, 2013

I would go with the 3.42 there's just more you can do with them.

For example when bds comes out with a lift for the 2014 sierra I'm going to lift mine. I only have 3.08's so I'm going to have to replace them with aftermarket whenever they come out. 3.08's I feel will put a lot of strain on the tranny with 35's.

Just me .02 go with 3.42's

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crushNchowda · October 18, 2013

E85 will get you 385/400+ on a stock 5.3 in the 2014s.

Sick

BringTheRain403 · October 18, 2013

If you wanna see how truly gutless the 3.08's are search for the towing test the guys at Fast Lane Truck did on youtube...

bcazier · October 18, 2013

Is there an RPO decoder for 3.42 and all the other codes? I am curious what I have that I might not know. Window sticker said 3.42 but no JL1.

MikeNH · October 18, 2013

Is there an RPO decoder for 3.42 and all the other codes? I am curious what I have that I might not know. Window sticker said 3.42 but no JL1.

There are RPO codes for just about everything on your truck. Axle related ones usually start with a G.

Chris · October 18, 2013

3.42 would be RPO GU6

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New2GMC · December 15, 2013

Hi everyone, I searched out the 3.08 and it wasn't easy to find. Everything that has a trailer package and snow plow package is 3.42. From what I can tell, 3.73 3,42 and 3.08 are all gear options in 4x4. I mostly carry myself and maybe 2 or 300 lbs. I searched out the tow package because I may tow 2000lbs tops 5 miles a few times a years. I also am getting the impression 5 and 6th gears are OD gearing ratios. So, If I wanted to tow a ton of weight.. couldn't I just lock out 6th gear? 5th on the 3.08 is slightly lower than 6th on the 3.42, less than the difference between 6th/ 3.42 and 6th 3.08. I also notices that the towing is about 2000lbs apart on each of all three gears ratios with 3.08 being the lowest.