Gas mileage hit 3.73 vs 3.42?

Slade8200 · October 20, 2016

Can anyone attest to how much worse it will be? I have a lead on a super clean truck but it has 3.73 and I have been only looking at 3.42 for highway driving / mpg reasons. It's an 06. Thanks.

Motostar929rr · October 20, 2016

Can anyone attest to how much worse it will be? I have a lead on a super clean truck but it has 3.73 and I have been only looking at 3.42 for highway driving / mpg reasons. It's an 06. Thanks.

I have the 3.42 in an ecsb z71 and usually get 17.9-18.5 on the highway. Dad has an 05 CCSB z71 with 3.73s. he gets up to 17+ on the highway. Unless you're driving massive amounts daily I don't think it's worth worrying about. FWIW, the 3.42 is good for hauling people and that's about it, it's a turd with a load, I mean, a small load, like a 6x10 single axle trailer with a single ATV on it. Lots of downshifting on the mildest of hills. I love the gearing in dad's ten times better than the 3.42s in mine...

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kstruckcountry · October 20, 2016

18 is about what mine will usually do on the highway. Without wind 18.5. Perfect gear ratio in my opinion.

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Nanotech Environmental · October 21, 2016

I have the 3.42 in an ecsb z71 and usually get 17.9-18.5 on the highway. Dad has an 05 CCSB z71 with 3.73s. he gets up to 17+ on the highway. Unless you're driving massive amounts daily I don't think it's worth worrying about. FWIW, the 3.42 is good for hauling people and that's about it, it's a turd with a load, I mean, a small load, like a 6x10 single axle trailer with a single ATV on it. Lots of downshifting on the mildest of hills. I love the gearing in dad's ten times better than the 3.42s in mine...

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I have the 3.42 in my 06 extcab 4x4 w5.3 and it tows just fine. Have often had 3-4 dirtbikes plus gear and people & I've found it to be reasonable in what it does, especially compared to what we drove 30 years ago. Have also towed over 3000lbs in steep hills and it did fine. Momentum is your friend.

Go drive a 1980ish fullsize 4x4 with all of ~160hp and tow the same things. Rough, noisy ride, horrific fuel mileage, and having it floored up every hill, praying you can maintain the speed limit. No thanks.

Slade8200 · October 28, 2016

I just drove over 1000 miles and 15 was the highest I got (cruising at 77-80). If I got 17 I could live with it.

kstruckcountry · October 28, 2016

To get 17 you'll have to drive 75 or lower. Knock it down to 70 and 17 is very doable with 3.42's or 3.73's.

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Slade8200 · October 28, 2016

I have these on as well... could they be robbing me?

kstruckcountry · October 28, 2016

I'd bet those 285's are probably costing 2 mpg or so.

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OLEREDRADO · November 2, 2016

I got 4.10s in a single cab z71 with 5.3. running stock tires I average around 16.5mpg.. I have to keep the highway speed down as I turn about 2300-2400 at 70...

rdnkcpa · November 2, 2016

I have a 2004 4X4 ECSB with a 5.3, 4L60E Trans, and a G80 3.73 Rear, bone stock. I run the stock size 16" P 245 tires. The best mileage I have ever experienced was 17 MPG, and that was on an extended highway trip running no more than 65. I was really, really trying to maximize mileage. It really usually gets 16ish.

kstruckcountry · November 2, 2016

I have a 2004 4X4 ECSB with a 5.3, 4L60E Trans, and a G80 3.73 Rear, bone stock. I run the stock size 16" P 245 tires. The best mileage I have ever experienced was 17 MPG, and that was on an extended highway trip running no more than 65. I was really, really trying to maximize mileage. It really usually gets 16ish.

I'm kind of curious what kind of roads you run on? For me, 17 highway is easily doable, even with some wind. And that's with everything in my sig.

Nanotech Environmental · November 3, 2016

I have a 2004 4X4 ECSB with a 5.3, 4L60E Trans, and a G80 3.73 Rear, bone stock. I run the stock size 16" P 245 tires. The best mileage I have ever experienced was 17 MPG, and that was on an extended highway trip running no more than 65. I was really, really trying to maximize mileage. It really usually gets 16ish.

This past summer on a trip, I got my best highway trip mileage yet; 26mpg CAD, or just over 21.5 mpg US.

2006 Sierra 4x4 Z71 EC 5.3 and 3.42. The truck had about ~185k miles on at the time. I also had a dirtbike in the back, as well as a bunch of other stuff. I kept my speed to around 63-65mph.

bgbdwlf2500 · November 4, 2016

Unloaded you wont notice much difference on the highway as far as mpg. If you don't drive a 3.73 truck you won't have anything to compare to. I've had 3.73, a lifted 3.42 and now I've got a 2010 crew 5.3 and 3.08. The 3.08 helps with mpg because of have to run over 100 mph to get the rpm to 2000. The lifted truck with 3.42 I just kept out of overdrive got 12mpg all the time. The 3.73 was very capable of getting 18 no problem. Its all in your driving habits and 1900 rpm seems to be the sweet spot for best cruising mpg

bgbdwlf2500 · November 4, 2016

On a 60 mph cruise on fairly level terrain my current truck with 3.08 will get 22 no problem, starts pushing 23

Nanotech Environmental · November 4, 2016

Unloaded you wont notice much difference on the highway as far as mpg. If you don't drive a 3.73 truck you won't have anything to compare to. I've had 3.73, a lifted 3.42 and now I've got a 2010 crew 5.3 and 3.08. The 3.08 helps with mpg because of have to run over 100 mph to get the rpm to 2000. The lifted truck with 3.42 I just kept out of overdrive got 12mpg all the time. The 3.73 was very capable of getting 18 no problem. Its all in your driving habits and 1900 rpm seems to be the sweet spot for best cruising mpg

Unloaded, in an apples to apples comparison, you will see difference of close to 10% between a 3.42 and 3.73.... For some, that is nothing. For others, it is significant.....