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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

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Old 10-19-2007, 08:54 AM
Stlheadake's Avatar
Stlheadake Stlheadake is offline
Join Date: Jan 2005
Location: St. Louis, Missouri (pronounced misery)
Posts: 203
Default I'd be careful...

Craig, I would be careful putting a programmer in that truck. From what I understand, you run the risk of clogging the DPF with a programmer. Not a cheap fix for more mileage.

I too have been in the 'hunt' for better mileage. My '06 doesn't do too bad 15 city and as high as 18-19 hwy (about 70mph). Still I feel it could/should do better.
St. Louis, MO

'06 Silverado K2500 4x4 Crew Cab D/A "Big Max" AmpResearch retractable Running Boards, 4" Turbo back Kennedy Exhaust, Kennedy Custom Tune!
'99 BMW K1200LT "Special K" my other "SUV"
'07 Salem by Forest River Fifth Wheel Toy Hauler
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Old 10-21-2007, 07:58 PM
RaiderCoach RaiderCoach is offline
Join Date: Oct 2007
Posts: 6
Unhappy mpg & programmer - not happy with LMM

I purchased an LMM crew cab 4wd in May. The fuel economy was never better than 16 mpg hwy and 13 hwy city. I lifted the truck and put 33" tires on it and hoped that it was a break in issue. My previous truck, an 03 duramax, would average 15 mpg city and up to 22 mpg hwy empty and 14 - 17 mpg hwy towing, varied depending on weight of load from 7000 to 12,000 lbs. I had an edge juice programmer on that truck. I recently put a Bully Dog Power Pup on this truck, really hoping for some mpg results. Being able to correct the speedo was nice, the truck didn't really need that much more power. No matter what the setting that I have the Bully Dog set to, I am averaging right at 13 mpg in town and 17 hwy. I have a very light right foot, so unless milage would increase with a heavy foot, I am probably at about where I'm going to be. Currently the truck has 9400 miles on it. I really miss my 03 and wish I had stayed with it.
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Old 10-22-2007, 06:53 PM
craigth craigth is offline
Join Date: Oct 2007
Posts: 7
Default Does GM know about the LMM MPG issue?

I lifted my truck with a ProComp 6" and 34" tires in Sept '07. You can see pictures in the TDP Photo Album page.

Interesting that you were able to adjust the speedo as the local GMC dealer said it couldn't be one with Allison transmissions! They also said that I couldn't have the tire pressure sensor set lower than 62PSI. However, a friend of mine with an '08 LMM 3500 said his dealership awas able to lower it in the 50PSI range. Not real happy with the knowledge and willingness to service non-standard features at the dealership.

Was the tuner worth it for performance? Did it make any noticable difference? Why did you select the Bully Dog tuner over another brand?

I wonder if GM knows about the LMM MPG issue?! I also wonder if this forum and the members of the TDP could use their numbers to communicate the issue and see if GM can tell us why and/or address the problem with some modifications.

It's really sad that in this time of high gas prices and diesel technology promoted as high mileage GM can't at least maintain or better yet increase the MPG of their LMM trucks. Most vehicles from year to year increase their MPG not decrease.

Maybe GM will get the wake up call they need when Toyota producesa 2500/3500 series of trucks with their own diesel! I'm sure their MPG will be high and more than likely the truck features and quality will be superior!
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Old 10-22-2007, 08:56 PM
RaiderCoach RaiderCoach is offline
Join Date: Oct 2007
Posts: 6
Default LMM and Tuner

I went with the Bully Dog because the sales manager at the dealership that I use recommended it. My previous tuner, in my 03, was an Edge Juice. It worked really well, but I did have some stalling problems so I decided to try this one. The Bully Dog does allow you to tune the speedo to your tire size, although I have not checked it to make sure that it really did anything. There is definetely a power difference, although for street driving without a load, I don't really feel that there's a need for the increase. I netted about 1 mpg increase, far below the 3 mpg increase that I realized with my 03 and the Edge product. I would not recommend spending the $500 for that small of an increase. I'll be taking my truck in for it's 10k oil change soon and will talk to the service manager about the milage issue, although I know the answer already that I'll get. It will be "We're not aware of anything wrong"? Always the same answer, until GM sends out a bulletin in about 6 months...
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Old 11-19-2007, 12:26 PM
Nolafishr Nolafishr is offline
Join Date: Nov 2007
Location: New Orleans
Posts: 15
Default Fuel Mileage

I am getting 17.8 MPG on mine, I topped off yesterday at half tank, I had 245 miles on the trip meter and it took 13.7 gals to top it off and I hand calculated the mileage and this is what I got. I did not check it against the DIC, Truck has 400 miles on it so far and still breaking in. I usually fill at half tank because it is a lil easier on the pocket at times, Diesel is at $3.24 a gallon here. I had it on the Highway with most of the mileage before I topped it off to see what it would do. I will keep a check on the Fuel mileage on it, so far I am happy with it.
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Old 11-21-2007, 09:03 PM
Runaway_Dmax Runaway_Dmax is offline
Join Date: Jan 2007
Location: Somewhere between WI & WY
Posts: 149
Exclamation guys posting on this site don't seem to have the luck/mpgs that the folks have over at the other site (DP) get..

I hope they are closer to what to expect than what I see here or I will be sadly disappointed in the new truck.
08 Blue Granite Silverado LTZ, DMax/Ally, CC/LB/4x4, Cab lights, Camper mirrors, Brake controller, Sunroof, Park assist, and skinny tires

06 Jetta TDI

00 Jayco 263RK (2nd home)

upgraded to an "09" Ranger 619VS/full windsheilds, w/an ETEC 225HO, T8 kicker, Minnkota 101 Terrova, and Lowrance electronics.

Real Trucks have LONG BEDS!
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Old 11-22-2007, 06:51 AM
Dakster Dakster is offline
Join Date: Jan 2007
Posts: 299

Here's what I have noticed. Each boards mileage claims vary as much (or more) than the mileage I actually get with my own truck. My normal everyday driving I get lousy mileage. Although, I take a lot of short trips and even my longer ones as on So. Florida parking lots (highways). The heat and being at or under sea level doesn't help either. (Doesn't make sense to me, but I get MUCH better fuel economy once I hit the rolling hills of GA and it stays that way until I get back home from Connecticut or in last years case Tennessee)

Obviously the LMM gets worse mileage than its predecessors, and from what I have expereinced and read it has a lot more power, and a restrictive exhaust too. The best case people seem to say about 1 mpg less and others up to 5-6 mpg less. My LMM gets better MPG than my gas 2007 6.0 Suburban (4x4) and 2005 Denali XL (AWD) and about the same as my 2005 Ford F250, 6.0 DIESEL, 4x4, CC, SB. Which is around 12 in local driving in town and 14-15 on highwy drives, but I drive fast 75-80. And yes, I wish I got better MPG's, but don't we all?
2007 Silverado, 3500HD, 4X4, CC, Long Bed, SRW, LMM Diesel, Navi, DVD, Roll-N-Lock Cover, ICI Running Boards, CoastalEtech GM Lockpick for DVD/Nav changes in Motion, Back-up Camera...

2006.5 VW Jetta Special Edition TDI - Blue Graphite - European Spec VW Fact. Nav Radio.
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Old 12-06-2007, 01:44 PM
snowsporter snowsporter is offline
Join Date: Dec 2007
Posts: 12
Default lmm fuel mileage

I had just purchased a dmax with the lmm engine. at just over 60 mph i am averaging almost 23 mpg highway. combination so far i am averaging around 17 mpg. first diesel and so far am impressed. i had just traded an 8.1 for the dmax that averaged highway 8 mpg, city around 6 mpg and towing 10k trailer 5mpg.
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Old 12-10-2007, 01:41 PM
kwtriton kwtriton is offline
Join Date: Dec 2007
Location: West Columbia, Texas
Posts: 1
Default Real Happy

Purchased an.. 07 NBS 4x4 4dr. short bed. Traded 01 xt-cab 4x4 D-Max w/300,000. The 01 constantly got 19 mpg on the hwy, New 07 is kind of strange and I am sure it has to do with the power curve. At 65 mph reset avg mpg truck gets about 16.5 mpg. run it up to 75 mph truck gets 21.8 to 22 mpg. I thought it was a fluke, but I have checked it several times and get the same results. Avg overall it has been running around 17.8 to 18.2 mpg, Truck now has 10,000 (+) and I am very satiisfied w/mpg.
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Old 12-11-2007, 05:36 PM
craigth craigth is offline
Join Date: Oct 2007
Posts: 7
Default Your the exception to the rule!

How are you calculating your MPG? Using the onboard ECU calculations or actual miles driven / gallons of fuel used? To be honest I don't trust the ECU calculations.

You definitely the exception to the rule. I'm still getting 10-11 MPG City / 13-14 Hwy, if I'm lucky. A friend of mine also has an '08 Chevy 3500 Crew LWB 4x4 that gets similar gas mileage to mine.

I would definitely like to know what the difference is and the secret to obtaining higher gas mileage. As I mentioned previously my '02 got MUCH BETTER MPG and I should of held onto it!

2008 GMC SLT 2500HD Crew Cab SWB 4WD ZLT
Black / Titanium
Sliding Rear Window
Integrated Trailer Brake
Billet Grill
Pro Comp 6" Lift Kit
Helo 17" Wheels
Nitto Terra Grappler 305/70/17 Tires
Spray-In Bedliner
Weather Guard Low Profile Aluminum Saddle Box
Remova-A-Ball Gooseneck Receiver
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