3.0L Duramax - who owns or has driven one

[Firetrout]

8 hours ago, BJ Niceguy said:

take this for what it is worth. When towing, mine uses a bunch of def compared to normal driving which makes sense. I drove 2500 miles not towing and gauge showed 1 bar above half. I towed about 400 mils and alert came on saying out of def. Refilled and it took 4.3 gallons. I bought a plug in scanner. It appears that the bar gauge shows full from 100% down to about 80% before moves. I have put in 2.5 gallon box and raised from 40% on scanner (50% on bar gauge) to 80% on scanner (full on bar gauge). On the scanner when gets down to 35-40% my bar gauge drops instantly from 1 bar below half to alarm. Not impressed at all with the gauge. My real concern is when towing being able to get full 2.5 gallon box in without getting so low I get alarm. Mine appears to use 1/2 gallon per hundred miles when towing hard (altitude, strong head winds, high speed) where engine runs 2500 rpm range. It appears to use 1/3 gallon per hundred miles when can hold mostly 1,700 RPM in 9th gear. Very little usage if driving without towing.

 

I took truck back to dealer. They let me set for couple hours, came out and said nothing wrong, and gave me a nice 5 page letter explaining that vehicle will use def if towing and a single sentence saying the gauge is not a normal float gauge. No further explanation as to how gauge works, just have a nice day. That is when I bought the scanner for phone recommended by others on this site. It is nice to see stuff, but really not necessary.

What scanner did you go with?

[Nick.C]

Does anyone have or driven a 3.0L with the Diesel off road pkg and the 3.73 gears ....Just wondering if any big advantage .

[topgear1224]

Does anyone have or driven a 3.0L with the Diesel off road pkg and the 3.73 gears ....Just wondering if any big advantage .

I own the 3.23 version and I can tell you that 3.73 are 100% worth it!

GM has programed the vehicle to limit torque in first gear below 3k Rpm. since the spread between first and second is pretty large the vehicle does not like to downshift into first gear so most of your rolling acceleration occurs in second and that's where 3.73 is going to absolutely beat the face in of a 3.23 truck.

don't be concerned about fuel economy. it's not going to change at all, in fact with 3.23s at 70 miles an hour (stock 20" all terrain's) is the lowest it can engage 10th gear, there's no gain in fuel economy between 9th and 10th, at that speed, because there is so much load because of the numerically low gears.

also if you plan on Towing you're only going to build about 12 to 13 lb of boost when trying to engine brake. The 3.73s are going to make the engine brake much more effective since it's multiplying the negative torque (engine braking). if you do mountains and you don't particularly like manually shifting and you just want to leave it in tow/haul mode you're going to have a much better Towing experience.

When I Maxed my truck out (15k GCWR) in order to stop it accelerating down the hills or at least slow the rate at which it tried to accelerate, I had to take manual control the transmission and engage the lowest possible gear. Even then had to drag my brakes down the 6%.

Overall other than the brake issue (shitty OEM pads)...... I do enjoy my 2020 GMC Sierra X31 elevation, but if I had to do it again, I would get the Chevy LT with the diesel off road package 1000%.

the Chevy has better aerodynamics, much better aftermarket bumper support, and it doesn't have cheap-looking satin-chrome finishes for no reason on the interior. Round Gauges are easier to read as well.

if you want to run larger tires and a lift Chevys can do 35s on a 4-inch where is the Sierra has to go all the way up to a six inch and requires a large amount of trimming. 3.73 is are also going to handle a larger tire much better. (Less performance loss)

the only use case I could see for not getting a 3.73 gear truck would be if you had a commute everyday in the 85 mile-an-hour zone in Texas, also with the higher gear ratios the g80 engages more predictably. This was very apparent on the V6 3.42 truck that I had as a loner.

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[Nick.C]

Thank you for all the info. I will be coming out of a 17 Denali with 6.2...3.23 ....8spd set up .....very enjoyable to drive. Had 5.3 ...3.42 ...6spd before that and wasn't all that impressed . Before that 6.6 Dmax  ....wish i never got rid of ....but can't really justify another 6.6.  Would have to order the 3.0 ...No dealer would ever put a truck together the way i want it .....i always liked the taller gears . 

[topgear1224]

Thank you for all the info. I will be coming out of a 17 Denali with 6.2...3.23 ....8spd set up .....very enjoyable to drive. Had 5.3 ...3.42 ...6spd before that and wasn't all that impressed . Before that 6.6 Dmax  ....wish i never got rid of ....but can't really justify another 6.6.  Would have to order the 3.0 ...No dealer would ever put a truck together the way i want it .....i always liked the taller gears . 

There really is no replacement for a steeper gear.

People will say "oh you don't really noticed the shallow gears because of the 10 speed" and although it makes it acceptable, If you lock them both in the same gear with the same load you'd be amazed how much better the 3.73 will accelerate.

Also you're buying a vehicle that's high torque low horsepower. Why not multiply your strength with that 3.73? and since horsepower is simply torque over time you're going to improve your high-end acceleration as well. Steeper gears also bring the gear spacing closer together meaning you're not going to have to work the truck anywhere near as hard (rpm wise) in day-to-day use.

I had no idea the diesel off-road package existed when I purchased my truck otherwise I would have ordered one.



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[Nick.C]

I'm a GMC guy also ....My lease is up in august and I have had my eye on the 3.0 for awhile ....was searching for trucks with 6 passenger ability and came across something with the 3.73 option ...so I followed that path to find they are hidden in that package . Kills me that you have to give up so much to have that 40/20/40 front seat . 

[Duramax3oh]

3 hours ago, Nick.C said:

I'm a GMC guy also ....My lease is up in august and I have had my eye on the 3.0 for awhile ....was searching for trucks with 6 passenger ability and came across something with the 3.73 option ...so I followed that path to find they are hidden in that package . Kills me that you have to give up so much to have that 40/20/40 front seat . 

Can you explain this a little more please? I love the 40/20/40 front bench so I got that. Have Z71 off-road package but don’t think I’ve seen the Z71 diesel package. What’s the easiest way for me to see what gear option I have?

[topgear1224]

Can you explain this a little more please? I love the 40/20/40 front bench so I got that. Have Z71 off-road package but don’t think I’ve seen the Z71 diesel package. What’s the easiest way for me to see what gear option I have?

Unless you bought the LT with the diesel off-road package you have 3.23.

even the AT4 3.0 gets 3.23

It's a $2,300 option here's what it includes.

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[Nick.C]

It is also available in the RST ....but you lose the bench seat as soon as you add 3.0 , but with 6.2 you can get bench as long as not leather ....go figure 

 

[redwngr]

10 hours ago, Duramax3oh said:

Can you explain this a little more please? I love the 40/20/40 front bench so I got that. Have Z71 off-road package but don’t think I’ve seen the Z71 diesel package. What’s the easiest way for me to see what gear option I have?

Another method, if you don't have the build sheet (which ANY dealer can run for you if they are given the VIN number). 

 

Download a QR code reader phone app and take a shot of the (QR square) on the silver/black sticker at the bottom of the door post.

QR code will give a bunch of, but not all, the build codes for the vehicle (typically the ones most likely needed for service/repair part purposes)

 

Then look for - 

GU5    Rear axle, 3.23 ratio
GU6    Rear axle, 3.42 ratio

 

GT4    Rear axle, 3.73 ratio
1 -  Included and only available with (BD1) Custom Max Trailering Package. 
2 -  Included and only available with (B4U) Diesel Off-Road Package.

 

BD1 is available on custom only

B4U is available on LT and RST only

Both include/require a bunch of other things in order to get the 3.73.

 

 

[Duramax3oh]

Thank you gents!

 

GU5 (3.23) it is. So would it be safe to say  the 3.23 is “worst” for towing but “best” for highway mpg? And 3.73 “best” for towing and “worst” for highway mpg?

Edited June 14, 2020 by Duramax3oh

[ullose272]

Thank you gents!
 
GU5 (3.23) it is. So would it be safe to say  the 3.23 is “worst” for towing but “best” for highway mpg? And 3.73 “best” for towing and “worst” for highway mpg?

I average about 23 mpg, mostly in town driving, 3.73 gears. I still get 27-30 mpg on the highway

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[topgear1224]

Thank you gents!
 
GU5 (3.23) it is. So would it be safe to say  the 3.23 is “worst” for towing but “best” for highway mpg? And 3.73 “best” for towing and “worst” for highway mpg?

Not really,

The biggest issue I have with 3.23s is that it can't stay in 10th gear and it can't even shift into 10th gear until 70 miles an hour. at 70 miles an hour if I lock it in 9th and then change it back to automatic so it engages 10th it's the same MPG on the same road. so there's no point in having that rear gear unless you live somewhere with an 85+ mile an hour speed limit.

I maxed out my truck to 15,000 lb GCWR and it was "fine" but the exhaust brake doesn't really help that much, it's better than not having one and freewheeling down the mountain, but it's doesn't work that well when you start moving anything over 7,000 pounds. on a long 6% grade I ended up having to drag my brakes even with manual downshifting and pulling over 4200 RPM.

3.73 is much better in this regards.

Are you planning on lifting it? 3.23s already feel undergeared for the 33in stock tire size.

I finally got to drive a diesel off-road package and now I'm debating whether or not I want to take the massive depreciation hit and trade my brand new truck that I've had for 4 months in for one.

The in gear acceleration goes from being "well at least it's efficient" to "hold up did I just spin in 2nd gear???"

I call the 3L "adequate" with the 3.23 but when you have 3.73s it genuinely becomes quick.

Also the 3.73 truck really liked to ride it's torque curve versus my truck which tries to ride its torque curve and then downshifts two gears.

Fuel economy for 3.73 and 3.23 is exactly the same.
You're not going to see a real world difference unless you're setting the cruise control at 90 miles an hour.


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[topgear1224]

I average about 23 mpg, mostly in town driving, 3.73 gears. I still get 27-30 mpg on the highway

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That basically what I get

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[Duramax3oh]

9 hours ago, topgear1224 said:

Not really....
 

Thanks for taking the time to explain that, very informative. Luckily I won’t even really notice because I kind of baby my truck. But in hindsight I wish I would have looked into that and will be mentioning this at least to people looking to purchase one.